diff --git a/.gitignore b/.gitignore
index 80152a5..05fe5a5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,5 @@ build
 .yotta.json
 yotta_modules
 yotta_targets
+*.swp
+Makefile
diff --git a/inc/ManagedString.h b/inc/ManagedString.h
index 81c06bf..bf2017c 100644
--- a/inc/ManagedString.h
+++ b/inc/ManagedString.h
@@ -1,7 +1,14 @@
 #ifndef MANAGED_STRING_H
 #define MANAGED_STRING_H
 
-#include "mbed.h"
+#include "RefCounted.h"
+
+struct StringData : RefCounted
+{
+    uint16_t len;
+    char data[0];
+};
+
 
 /**
   * Class definition for a ManagedString.
@@ -14,21 +21,43 @@
   * 1) std::shared_ptr is not yet availiable on the ARMCC compiler
   * 2) to reduce memory footprint - we don't need many of the other features in the std library
   * 3) it makes an interestin case study for anyone interested in seeing how it works!
+  * 4) we need explicit reference counting to inter-op with low-level application langauge runtimes
+  * 5) the reference counting needs to also work for read-only, flash-resident strings
   */
 class ManagedString
 {
-    // Internally we record the string as a char *, but control access to this to proide immutability
-    // and reference counting.
-    char *data;
-    int16_t *ref;
-    int16_t len;
+    // StringData contains the reference count, the length, follwed by char[] data, all in one block.
+    // When referece count is 0xffff, then it's read only and should not be counted.
+    // Otherwise the block was malloc()ed.
+    // We control access to this to proide immutability and reference counting.
+    StringData *ptr;
 
     public:
 
+    /**
+      * Constructor. 
+      * Create a managed string from a specially prepared string literal. It will ptr->incr().
+      *
+      * @param ptr The literal - first two bytes should be 0xff, then the length in little endian, then the literal. The literal has to be 4-byte aligned.
+      * 
+      * Example:
+      * @code 
+      * static const char hello[] __attribute__ ((aligned (4))) = "\xff\xff\x05\x00" "Hello";
+      * ManagedString s((StringData*)(void*)hello);
+      * @endcode
+      */    
+    ManagedString(StringData *ptr);
+
+    /**
+      * Get current ptr, do not decr() it, and set the current instance to empty string.
+      * This is to be used by specialized runtimes which pass StringData around.
+      */
+    StringData *leakData();
+
     /**
       * Constructor. 
       * Create a managed string from a pointer to an 8-bit character buffer.
-      * The buffer is copied to ensure sage memory management (the supplied
+      * The buffer is copied to ensure safe memory management (the supplied
       * character buffer may be decalred on the stack for instance).
       *
       * @param str The character array on which to base the new ManagedString.
@@ -115,7 +144,7 @@ class ManagedString
       *
       * Free this ManagedString, and decrement the reference count to the
       * internal character buffer. If we're holding the last reference,
-      * also free the character buffer and reference counter.
+      * also free the character buffer.
       */
     ~ManagedString();
     
@@ -251,11 +280,14 @@ class ManagedString
 
 
     /**
-      * Provides an immutable 8 bit wide haracter buffer representing this string.
+      * Provides an immutable 8 bit wide character buffer representing this string.
       *
       * @return a pointer to the character buffer.
       */    
-    const char *toCharArray();
+    const char *toCharArray() const
+    {
+        return ptr->data;
+    }
     
     /**
       * Determines the length of this ManagedString in characters.
@@ -269,7 +301,10 @@ class ManagedString
       * print(s.length()) // prints "4"
       * @endcode
       */ 
-    int16_t length();
+    int16_t length() const
+    {
+        return ptr->len;
+    }
 
     /**
       * Empty String constant
diff --git a/inc/MicroBitImage.h b/inc/MicroBitImage.h
index bb5af02..26aabea 100644
--- a/inc/MicroBitImage.h
+++ b/inc/MicroBitImage.h
@@ -2,6 +2,14 @@
 #define MICROBIT_IMAGE_H
 
 #include "mbed.h"
+#include "RefCounted.h"
+
+struct ImageData : RefCounted
+{
+    uint16_t width;     // Width in pixels
+    uint16_t height;    // Height in pixels
+    uint8_t data[0];    // 2D array representing the bitmap image
+};
 
 /**
   * Class definition for a MicroBitImage.
@@ -11,9 +19,7 @@
   */
 class MicroBitImage
 {
-    int16_t width;                               // Width of the bitmap, in pixels.
-    int16_t height;                              // Height of the bitmap, in pixels.
-    int16_t *ref;                                // Reference count.
+    ImageData *ptr;     // Pointer to payload data
     
     
     /**
@@ -32,7 +38,34 @@ class MicroBitImage
     
     public:
     static MicroBitImage EmptyImage;    // Shared representation of a null image.
-    uint8_t *bitmap;                    // 2D array representing the bitmap image.    
+
+    /**
+      * Get current ptr, do not decr() it, and set the current instance to empty image.
+      * This is to be used by specialized runtimes which pass ImageData around.
+      */
+    ImageData *leakData();
+
+    /**
+      * Return a 2D array representing the bitmap image.
+      */
+    uint8_t *getBitmap()
+    {
+        return ptr->data;
+    }
+    
+    /**
+      * Constructor. 
+      * Create an image from a specially prepared constant array, with no copying. Will call ptr->incr().
+      *
+      * @param ptr The literal - first two bytes should be 0xff, then width, 0, height, 0, and the bitmap. Width and height are 16 bit. The literal has to be 4-byte aligned.
+      * 
+      * Example:
+      * @code 
+      * static const uint8_t heart[] __attribute__ ((aligned (4))) = { 0xff, 0xff, 10, 0, 5, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, }; // a cute heart
+      * MicroBitImage i((ImageData*)(void*)heart);
+      * @endcode
+      */
+    MicroBitImage(ImageData *ptr);
     
     /**
       * Default Constructor. 
@@ -325,7 +358,10 @@ class MicroBitImage
       * i.getWidth(); //equals 10...
       * @endcode
       */
-    int getWidth();
+    int getWidth() const
+    {
+        return ptr->width;
+    }
 
     /**
       * Gets the height of this image.
@@ -339,8 +375,28 @@ class MicroBitImage
       * i.getHeight(); //equals 5...
       * @endcode
       */
-    int getHeight();
+    int getHeight() const
+    {
+        return ptr->height;
+    }
     
+    /**
+      * Gets number of bytes in the bitmap, ie., width * height.
+      *
+      * @return The size of the bitmap.
+      * 
+      * Example:
+      * @code
+      * const uint8_t heart[] = { 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, }; // a cute heart
+      * MicroBitImage i(10,5,heart);
+      * i.getSize(); //equals 50...
+      * @endcode
+      */
+    int getSize() const
+    {
+        return ptr->width * ptr->height;
+    }
+
     /**
       * Converts the bitmap to a csv string.
       *
@@ -352,7 +408,7 @@ class MicroBitImage
       * @endcode
       */
     ManagedString toString();
-    
+
     /**
       * Crops the image to the given dimensions
       *
@@ -372,6 +428,17 @@ class MicroBitImage
       */
     MicroBitImage crop(int startx, int starty, int finx, int finy);
 
+    /**
+      * Check if image is read-only (i.e., residing in flash).
+      */
+    bool isReadOnly();
+
+    /**
+      * Create a copy of the image bitmap. Used particularly, when isReadOnly() is true.
+      *
+      * @return an instance of MicroBitImage which can be modified independently of the current instance
+      */
+    MicroBitImage clone();
 };
 
 #endif
diff --git a/inc/RefCounted.h b/inc/RefCounted.h
new file mode 100644
index 0000000..9d332ad
--- /dev/null
+++ b/inc/RefCounted.h
@@ -0,0 +1,34 @@
+#ifndef REF_COUNTED_H
+#define REF_COUNTED_H
+
+#include "mbed.h"
+
+/**
+  * Base class for payload for ref-counted objects. Used by ManagedString and MicroBitImage.
+  * There is no constructor, as this struct is typically malloc()ed.
+  */
+struct RefCounted
+{
+public:
+    /**
+      * The high 15 bits hold the number of outstanding references. The lowest bit is always 1
+      * to make sure it doesn't look like vtable.
+      * Should never be even or one (object should be deleted then).
+      * When it's set to 0xffff, it means the object sits in flash and should not be counted.
+      */
+    uint16_t refCount;
+
+    /** Increment reference count. */
+    void incr();
+
+    /** Decrement reference count. */
+    void decr();
+
+    /** Initializes for one outstanding reference. */
+    void init();
+
+    /** Checks if the object sits in flash memory. */
+    bool isReadOnly();
+};
+
+#endif
diff --git a/source/CMakeLists.txt b/source/CMakeLists.txt
index 8d16619..47faf72 100755
--- a/source/CMakeLists.txt
+++ b/source/CMakeLists.txt
@@ -28,6 +28,7 @@ set(YOTTA_AUTO_MICROBIT-DAL_CPP_FILES
     "MicroBitSerial.cpp"
     "MicroBitHeapAllocator.cpp"
     "MicroBitListener.cpp"
+    "RefCounted.cpp"
     "MemberFunctionCallback.cpp"
     "ble-services/MicroBitDFUService.cpp"
     "ble-services/MicroBitEventService.cpp"
diff --git a/source/ManagedString.cpp b/source/ManagedString.cpp
index 829b65a..e200ce0 100644
--- a/source/ManagedString.cpp
+++ b/source/ManagedString.cpp
@@ -3,6 +3,7 @@
 #include "mbed.h"
 #include "MicroBit.h"
 
+static const char empty[] __attribute__ ((aligned (4))) = "\xff\xff\0\0\0";
 
 /**
   * Internal constructor helper.
@@ -10,11 +11,7 @@
   */
 void ManagedString::initEmpty()
 {
-    data = ManagedString::EmptyString.data;
-    ref = ManagedString::EmptyString.ref;
-    len = ManagedString::EmptyString.len;
-
-    (*ref)++;
+    ptr = (StringData*)(void*)empty;
 }
 
 /**
@@ -25,13 +22,41 @@ void ManagedString::initString(const char *str)
 {   
     // Initialise this ManagedString as a new string, using the data provided.
     // We assume the string is sane, and null terminated.
-    len = strlen(str);
-    data = (char *) malloc(len+1);
-    memcpy(data, str, len+1);
-    ref = (int16_t *) malloc(sizeof(int16_t));
-    *ref = 1;
+    int len = strlen(str);
+    ptr = (StringData *) malloc(4+len+1);
+    ptr->init();
+    ptr->len = len;
+    memcpy(ptr->data, str, len+1);
 }
 
+/**
+  * Constructor. 
+  * Create a managed string from a specially prepared string literal. It will ptr->incr().
+  *
+  * @param ptr The literal - first two bytes should be 0xff, then the length in little endian, then the literal. The literal has to be 4-byte aligned.
+  * 
+  * Example:
+  * @code 
+  * static const char hello[] __attribute__ ((aligned (4))) = "\xff\xff\x05\x00" "Hello";
+  * ManagedString s((StringData*)(void*)hello);
+  * @endcode
+  */    
+ManagedString::ManagedString(StringData *p)
+{
+    ptr = p;
+    ptr->incr();
+}
+
+/**
+  * Get current ptr, do not decr() it, and set the current instance to empty string.
+  * This is to be used by specialized runtimes which pass StringData around.
+  */
+StringData* ManagedString::leakData()
+{
+    StringData *res = ptr;
+    initEmpty();
+    return res;
+}
 
 /**
   * Constructor. 
@@ -65,7 +90,6 @@ ManagedString::ManagedString(const int value)
   */      
 ManagedString::ManagedString(const char value)
 {
-
     char str[2] = {value, 0};
     initString(str); 
 }
@@ -82,7 +106,7 @@ ManagedString::ManagedString(const char value)
 ManagedString::ManagedString(const char *str)
 {
     // Sanity check. Return EmptyString for anything distasteful
-    if ((str == NULL || *str == 0) && this != &ManagedString::EmptyString)
+    if (str == NULL || *str == 0)
     {
         initEmpty();
         return;
@@ -94,19 +118,17 @@ ManagedString::ManagedString(const char *str)
 ManagedString::ManagedString(const ManagedString &s1, const ManagedString &s2)
 {
     // Calculate length of new string.
-    len = s1.len + s2.len;
+    int len = s1.length() + s2.length();
 
     // Create a new buffer for holding the new string data.
-    data = (char *) malloc(len+1);
+    ptr = (StringData*) malloc(4+len+1);
+    ptr->init();
+    ptr->len = len;
 
     // Enter the data, and terminate the string.
-    memcpy(data, s1.data, s1.len);
-    memcpy(data + s1.len, s2.data, s2.len);
-    data[len] = 0;
-
-    // Initialise the ref count and we're done.
-    ref = (int16_t *) malloc(sizeof(int16_t));
-    *ref = 1;
+    memcpy(ptr->data, s1.toCharArray(), s1.length());
+    memcpy(ptr->data + s1.length(), s2.toCharArray(), s2.length());
+    ptr->data[len] = 0;
 }
 
 
@@ -133,17 +155,14 @@ ManagedString::ManagedString(const char *str, const int16_t length)
         return;
     }
 
-    // Store the length of the new string
-    len = length;
     
     // Allocate a new buffer, and create a NULL terminated string.
-    data = (char *) malloc(len+1);
-    memcpy(data, str, len);
-    data[len] = 0;
-
-    // Initialize a refcount and we're done.
-    ref = (int16_t *) malloc(sizeof(int16_t));
-    *ref = 1;
+    ptr = (StringData*) malloc(4+length+1);
+    ptr->init();
+    // Store the length of the new string
+    ptr->len = length;
+    memcpy(ptr->data, str, length);
+    ptr->data[length] = 0;
 }
 
 /**
@@ -161,11 +180,8 @@ ManagedString::ManagedString(const char *str, const int16_t length)
   */
 ManagedString::ManagedString(const ManagedString &s)
 {
-    data = s.data;
-    ref = s.ref;
-    len = s.len;
-
-    (*ref)++;
+    ptr = s.ptr;
+    ptr->incr();
 }
 
 
@@ -193,11 +209,7 @@ ManagedString::ManagedString()
   */
 ManagedString::~ManagedString()
 {
-    if(--(*ref) == 0)
-    {
-        free(data);
-        free(ref);
-    }
+    ptr->decr();
 }
 
 /**
@@ -220,19 +232,12 @@ ManagedString::~ManagedString()
   */
 ManagedString& ManagedString::operator = (const ManagedString& s)
 {
-    if(this == &s)
+    if (this->ptr == s.ptr)
         return *this; 
 
-    if(--(*ref) == 0)
-    {
-        free(data);
-        free(ref);
-    }
-    
-    data = s.data;
-    ref = s.ref;
-    len = s.len;
-    (*ref)++;
+    ptr->decr();
+    ptr = s.ptr;
+    ptr->incr();
 
     return *this;
 }
@@ -258,7 +263,7 @@ ManagedString& ManagedString::operator = (const ManagedString& s)
   */
 bool ManagedString::operator== (const ManagedString& s)
 {
-    return ((len == s.len) && (memcmp(data,s.data,len)==0));    
+    return ((length() == s.length()) && (strcmp(toCharArray(),s.toCharArray())==0));
 }
 
 /**
@@ -282,7 +287,7 @@ bool ManagedString::operator== (const ManagedString& s)
   */
 bool ManagedString::operator< (const ManagedString& s)
 {
-    return (memcmp(data, s.data,min(len,s.len))<0);
+    return (strcmp(toCharArray(), s.toCharArray())<0);
 }
 
 /**
@@ -306,7 +311,7 @@ bool ManagedString::operator< (const ManagedString& s)
   */
 bool ManagedString::operator> (const ManagedString& s)
 {
-    return (memcmp(data, s.data,min(len,s.len))>0); 
+    return (strcmp(toCharArray(), s.toCharArray())>0);
 }
 
 /**
@@ -326,14 +331,14 @@ bool ManagedString::operator> (const ManagedString& s)
 ManagedString ManagedString::substring(int16_t start, int16_t length)
 {
     // If the parameters are illegal, just return a reference to the empty string.
-    if (start >= len)
+    if (start >= this->length())
         return ManagedString(ManagedString::EmptyString);
 
     // Compute a safe copy length;
-    length = min(len-start, length);
+    length = min(this->length()-start, length);
 
     // Build a ManagedString from this.
-    return ManagedString(data+start, length);
+    return ManagedString(toCharArray()+start, length);
 }
 
 /**
@@ -353,19 +358,13 @@ ManagedString ManagedString::substring(int16_t start, int16_t length)
 ManagedString ManagedString::operator+ (ManagedString& s)
 {
     // If the other string is empty, nothing to do!
-    if(s.len == 0)
+    if(s.length() == 0)
         return *this;
 
-    if (len == 0)
-        return s;
-        
-    if(s == ManagedString::EmptyString)
-        return *this;
-        
-    if(*this == ManagedString::EmptyString)
+    if (length() == 0)
         return s;
 
-    return ManagedString(data, s.data);
+    return ManagedString(*this, s);
 }
 
 
@@ -384,39 +383,10 @@ ManagedString ManagedString::operator+ (ManagedString& s)
   */     
 char ManagedString::charAt(int16_t index)
 {
-    return (index >=0 && index < len) ? data[index] : 0;
-}
-
-/**
-  * Provides an immutable 8 bit wide haracter buffer representing this string.
-  *
-  * @return a pointer to the charcter buffer.
-  */    
-const char *ManagedString::toCharArray()
-{
-    return data;
-}
-
-/**
-  * Determines the length of this ManagedString in characters.
-  *
-  * @return the length of the string in characters.
-  *
-  * Example:
-  * @code 
-  * ManagedString s("abcd");
-  *
-  * print(s.length()) // prints "4"
-  * @endcode
-  */ 
-int16_t ManagedString::length()
-{
-    return len;
+    return (index >=0 && index < length()) ? ptr->data[index] : 0;
 }
 
 /**
   * Empty string constant literal
   */
-ManagedString ManagedString::EmptyString("\0");
-
-
+ManagedString ManagedString::EmptyString((StringData*)(void*)empty);
diff --git a/source/MicroBit.cpp b/source/MicroBit.cpp
index ed8d38d..b3367b2 100644
--- a/source/MicroBit.cpp
+++ b/source/MicroBit.cpp
@@ -122,7 +122,9 @@ void MicroBit::init()
 #endif
 
 #if CONFIG_ENABLED(MICROBIT_BLE_DEVICE_INFORMATION_SERVICE)
-    DeviceInformationService ble_device_information_service (*ble, MICROBIT_BLE_MANUFACTURER, MICROBIT_BLE_MODEL, getSerial().toCharArray(), MICROBIT_BLE_HARDWARE_VERSION, MICROBIT_BLE_FIRMWARE_VERSION, MICROBIT_BLE_SOFTWARE_VERSION);
+    // Create a temporary, so that compiler doesn't delete the pointer before DeviceInformationService copies it
+    ManagedString tmp = getSerial();
+    DeviceInformationService ble_device_information_service (*ble, MICROBIT_BLE_MANUFACTURER, MICROBIT_BLE_MODEL, tmp.toCharArray(), MICROBIT_BLE_HARDWARE_VERSION, MICROBIT_BLE_FIRMWARE_VERSION, MICROBIT_BLE_SOFTWARE_VERSION);
 #endif
 
 #if CONFIG_ENABLED(MICROBIT_BLE_EVENT_SERVICE)
@@ -233,7 +235,7 @@ ManagedString MicroBit::getSerial()
     ManagedString s1 = ManagedString(n1);
     ManagedString s2 = ManagedString(n2);
 
-    return s1+s2;
+    return s1 + s2;
 }
 
 /**
diff --git a/source/MicroBitDisplay.cpp b/source/MicroBitDisplay.cpp
index 1337071..1513c10 100644
--- a/source/MicroBitDisplay.cpp
+++ b/source/MicroBitDisplay.cpp
@@ -126,7 +126,7 @@ void MicroBitDisplay::render()
                 y = height - 1 - t;
         }
         
-        if(image.bitmap[y*(width*2)+x])
+        if(image.getBitmap()[y*(width*2)+x])
             coldata |= (1 << i);
     }
                     
@@ -175,7 +175,7 @@ void MicroBitDisplay::renderGreyscale()
                 y = height - 1 - t;
         }
         
-        if(min(image.bitmap[y * (width * 2) + x],brightness) & greyscaleBitMsk)
+        if(min(image.getBitmap()[y * (width * 2) + x],brightness) & greyscaleBitMsk)
             coldata |= (1 << i);
     }            
     //write the new bit pattern
diff --git a/source/MicroBitHeapAllocator.cpp b/source/MicroBitHeapAllocator.cpp
index 36cf1d0..965e893 100644
--- a/source/MicroBitHeapAllocator.cpp
+++ b/source/MicroBitHeapAllocator.cpp
@@ -77,7 +77,7 @@ void microbit_heap_print(HeapDefinition &heap)
 	while (block < heap.heap_end)
 	{
 		blockSize = *block & ~MICROBIT_HEAP_BLOCK_FREE;
-        uBit.serialpc.printf("[%C:%d] ", *block & MICROBIT_HEAP_BLOCK_FREE ? 'F' : 'U', blockSize*4);
+        uBit.serial.printf("[%C:%d] ", *block & MICROBIT_HEAP_BLOCK_FREE ? 'F' : 'U', blockSize*4);
         if (cols++ == 20)
         {
             uBit.serial.printf("\n");
@@ -329,7 +329,7 @@ void *microbit_malloc(size_t size)
             if (p != NULL)
             {
 #if CONFIG_ENABLED(MICROBIT_DBG) && CONFIG_ENABLED(MICROBIT_HEAP_DBG)
-                pc.uBit.serial("microbit_malloc: ALLOCATED: %d [%p]\n", size, p);
+                uBit.serial.printf("microbit_malloc: ALLOCATED: %d [%p]\n", size, p);
 #endif    
                 return p;
             }
@@ -345,7 +345,7 @@ void *microbit_malloc(size_t size)
 #if CONFIG_ENABLED(MICROBIT_DBG) && CONFIG_ENABLED(MICROBIT_HEAP_DBG)
         // Keep everything trasparent if we've not been initialised yet
         if (microbit_active_heaps())
-            pc.uBit.serial("microbit_malloc: NATIVE ALLOCATED: %d [%p]\n", size, p);
+            uBit.serial.printf("microbit_malloc: NATIVE ALLOCATED: %d [%p]\n", size, p);
 #endif    
         return p;
     }
@@ -354,7 +354,7 @@ void *microbit_malloc(size_t size)
 #if CONFIG_ENABLED(MICROBIT_DBG) && CONFIG_ENABLED(MICROBIT_HEAP_DBG)
     // Keep everything trasparent if we've not been initialised yet
     if (microbit_active_heaps())
-        pc.uBit.serial("microbit_malloc: OUT OF MEMORY\n");
+        uBit.serial.printf("microbit_malloc: OUT OF MEMORY\n");
 #endif    
     
 #if CONFIG_ENABLED(MICROBIT_PANIC_HEAP_FULL)
@@ -375,7 +375,7 @@ void microbit_free(void *mem)
 
 #if CONFIG_ENABLED(MICROBIT_DBG) && CONFIG_ENABLED(MICROBIT_HEAP_DBG)
     if (microbit_active_heaps())
-        pc.uBit.serial("microbit_free:   %p\n", mem);
+        uBit.serial.printf("microbit_free:   %p\n", mem);
 #endif    
     // Sanity check.
 	if (memory == NULL)
diff --git a/source/MicroBitImage.cpp b/source/MicroBitImage.cpp
index 43a8a93..686450e 100644
--- a/source/MicroBitImage.cpp
+++ b/source/MicroBitImage.cpp
@@ -7,10 +7,12 @@
 
 #include "MicroBit.h"
 
+
 /*
  * The null image. We actally create a small one byte buffer here, just to keep NULL pointers out of the equation.
  */
-MicroBitImage MicroBitImage::EmptyImage(1,1);
+static const uint16_t empty[] __attribute__ ((aligned (4))) = { 0xffff, 1, 1, 0, };
+MicroBitImage MicroBitImage::EmptyImage((ImageData*)(void*)empty);
 
 /**
   * Default Constructor. 
@@ -65,12 +67,8 @@ MicroBitImage::MicroBitImage(const int16_t x, const int16_t y)
   */
 MicroBitImage::MicroBitImage(const MicroBitImage &image)
 {
-    bitmap = image.bitmap;
-    width = image.width;
-    height = image.height;
-    ref = image.ref;
-
-    (*ref)++;  
+    ptr = image.ptr;
+    ptr->incr();
 }
 
 /**
@@ -138,17 +136,12 @@ MicroBitImage::MicroBitImage(const char *s)
         parseReadPtr++;
     }
 
-    // Store the geomtery.
-    this->width = width;
-    this->height = height;
-    this->bitmap = (uint8_t *) malloc(width * height);
-    this->ref = (int16_t *) malloc(sizeof(int16_t));
-    *ref = 1;
+    this->init(width, height, NULL);
 
     // Second pass: collect the data.
     parseReadPtr = s;
     parseWritePtr = parseBuf;
-    bitmapPtr = this->bitmap;
+    bitmapPtr = this->getBitmap();
 
     while (*parseReadPtr)
     {
@@ -172,6 +165,36 @@ MicroBitImage::MicroBitImage(const char *s)
     }
 }
 
+/**
+  * Constructor. 
+  * Create an image from a specially prepared constant array, with no copying. Will call ptr->incr().
+  *
+  * @param ptr The literal - first two bytes should be 0xff, then width, 0, height, 0, and the bitmap. Width and height are 16 bit. The literal has to be 4-byte aligned.
+  * 
+  * Example:
+  * @code 
+  * static const uint8_t heart[] __attribute__ ((aligned (4))) = { 0xff, 0xff, 10, 0, 5, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, }; // a cute heart
+  * MicroBitImage i((ImageData*)(void*)heart);
+  * @endcode
+  */
+MicroBitImage::MicroBitImage(ImageData *p)
+{
+    ptr = p;
+    ptr->incr();
+}
+    
+/**
+  * Get current ptr, do not decr() it, and set the current instance to empty image.
+  * This is to be used by specialized runtimes which pass ImageData around.
+  */
+ImageData *MicroBitImage::leakData()
+{
+    ImageData* res = ptr;
+    init_empty();
+    return res;
+}
+
+
 /**
   * Constructor. 
   * Create a bitmap representation of a given size, based on a given buffer.
@@ -197,11 +220,7 @@ MicroBitImage::MicroBitImage(const int16_t x, const int16_t y, const uint8_t *bi
   */
 MicroBitImage::~MicroBitImage()
 {
-    if(--(*ref) == 0)
-    {
-        free(bitmap);
-        free(ref);
-    }
+    ptr->decr();
 }
 
 /**
@@ -209,12 +228,7 @@ MicroBitImage::~MicroBitImage()
   */
 void MicroBitImage::init_empty()
 {   
-    bitmap = MicroBitImage::EmptyImage.bitmap;
-    width = MicroBitImage::EmptyImage.width;
-    height = MicroBitImage::EmptyImage.height;
-    ref = MicroBitImage::EmptyImage.ref;
-    
-    (*ref)++;
+    ptr = (ImageData*)(void*)empty;
 }
 
 /**
@@ -232,23 +246,21 @@ void MicroBitImage::init(const int16_t x, const int16_t y, const uint8_t *bitmap
         init_empty();
         return; 
     }    
+
     
     // Create a copy of the array
-    this->width = x;
-    this->height = y;
+    ptr = (ImageData*)malloc(4 + x * y);
+    ptr->init();
+    ptr->width = x;
+    ptr->height = y;
     
     // create a linear buffer to represent the image. We could use a jagged/2D array here, but experimentation
     // showed this had a negative effect on memory management (heap fragmentation etc).
      
-    this->bitmap = (uint8_t *) malloc(width*height);
-
     if (bitmap)
         this->printImage(x,y,bitmap);
     else
         this->clear();
-        
-    ref = (int16_t *) malloc(sizeof(int16_t));
-    *ref = 1;
 }
 
 /**
@@ -271,21 +283,12 @@ void MicroBitImage::init(const int16_t x, const int16_t y, const uint8_t *bitmap
   */
 MicroBitImage& MicroBitImage::operator = (const MicroBitImage& i)
 {
-    if(this == &i)
+    if(ptr == i.ptr)
         return *this;
 
-    if(--(*ref) == 0)
-    {
-        free(bitmap);
-        free(ref);
-    }
-
-    bitmap = i.bitmap;
-    width = i.width;
-    height = i.height;
-    ref = i.ref;
-    
-    (*ref)++;
+    ptr->decr();
+    ptr = i.ptr;
+    ptr->incr();
 
     return *this;
 }
@@ -309,10 +312,10 @@ MicroBitImage& MicroBitImage::operator = (const MicroBitImage& i)
   */
 bool MicroBitImage::operator== (const MicroBitImage& i)
 {
-    if (bitmap == i.bitmap)
+    if (ptr == i.ptr)
         return true;
     else
-        return ((width == i.width) && (height == i.height) && (memcmp(bitmap, i.bitmap,width*height)==0));    
+        return (ptr->width == i.ptr->width && ptr->height == i.ptr->height && (memcmp(getBitmap(), i.ptr->data, getSize())==0));    
 }
 
 
@@ -327,7 +330,7 @@ bool MicroBitImage::operator== (const MicroBitImage& i)
   */
 void MicroBitImage::clear()
 {
-    memclr(this->bitmap, width*height);
+    memclr(getBitmap(), getSize());
 }
  
 /**
@@ -346,10 +349,10 @@ void MicroBitImage::clear()
 int MicroBitImage::setPixelValue(int16_t x , int16_t y, uint8_t value)
 {
     //sanity check
-    if(x >= width || y >= height || x < 0 || y < 0)
+    if(x >= getWidth() || y >= getHeight() || x < 0 || y < 0)
         return MICROBIT_INVALID_PARAMETER;
     
-    this->bitmap[y*width+x] = value;
+    this->getBitmap()[y*getWidth()+x] = value;
     return MICROBIT_OK;
 }
 
@@ -369,10 +372,10 @@ int MicroBitImage::setPixelValue(int16_t x , int16_t y, uint8_t value)
 int MicroBitImage::getPixelValue(int16_t x , int16_t y)
 {
     //sanity check
-    if(x >= width || y >= height || x < 0 || y < 0)
+    if(x >= getWidth() || y >= getHeight() || x < 0 || y < 0)
         return MICROBIT_INVALID_PARAMETER;
     
-    return this->bitmap[y*width+x];
+    return this->getBitmap()[y*getWidth()+x];
 }
 
 /**
@@ -403,18 +406,18 @@ int MicroBitImage::printImage(int16_t width, int16_t height, const uint8_t *bitm
         return MICROBIT_INVALID_PARAMETER;
 
     // Calcualte sane start pointer.
-    pixelsToCopyX = min(width,this->width);
-    pixelsToCopyY = min(height,this->height);
+    pixelsToCopyX = min(width,this->getWidth());
+    pixelsToCopyY = min(height,this->getHeight());
 
     pIn = bitmap;
-    pOut = this->bitmap;
+    pOut = this->getBitmap();
     
     // Copy the image, stride by stride.
     for (int i=0; i<pixelsToCopyY; i++)
     {
         memcpy(pOut, pIn, pixelsToCopyX);
         pIn += width;
-        pOut += this->width;
+        pOut += this->getWidth();
     }
 
     return MICROBIT_OK;
@@ -445,21 +448,21 @@ int MicroBitImage::paste(const MicroBitImage &image, int16_t x, int16_t y, uint8
 
     // Sanity check.
     // We permit writes that overlap us, but ones that are clearly out of scope we can filter early.
-    if (x >= width || y >= height || x+image.width <= 0 || y+image.height <= 0)
+    if (x >= getWidth() || y >= getHeight() || x+image.getWidth() <= 0 || y+image.getHeight() <= 0)
         return 0;
 
     //Calculate the number of byte we need to copy in each dimension.
-    cx = x < 0 ? min(image.width + x, width) : min(image.width, width - x);
-    cy = y < 0 ? min(image.height + y, height) : min(image.height, height - y);
+    cx = x < 0 ? min(image.getWidth() + x, getWidth()) : min(image.getWidth(), getWidth() - x);
+    cy = y < 0 ? min(image.getHeight() + y, getHeight()) : min(image.getHeight(), getHeight() - y);
 
     // Calculate sane start pointer.
-    pIn = image.bitmap;
+    pIn = image.ptr->data;
     pIn += (x < 0) ? -x : 0;
-    pIn += (y < 0) ? -image.width*y : 0;
+    pIn += (y < 0) ? -image.getWidth()*y : 0;
     
-    pOut = bitmap;
+    pOut = getBitmap();
     pOut += (x > 0) ? x : 0;
-    pOut += (y > 0) ? width*y : 0;
+    pOut += (y > 0) ? getWidth()*y : 0;
 
     // Copy the image, stride by stride
     // If we want primitive transparecy, we do this byte by byte.
@@ -478,8 +481,8 @@ int MicroBitImage::paste(const MicroBitImage &image, int16_t x, int16_t y, uint8
                 }
             }
     
-            pIn += image.width;
-            pOut += width;
+            pIn += image.getWidth();
+            pOut += getWidth();
         }
     }
     else
@@ -489,8 +492,8 @@ int MicroBitImage::paste(const MicroBitImage &image, int16_t x, int16_t y, uint8
             memcpy(pOut, pIn, cx);
 
             pxWritten += cx;
-            pIn += image.width;
-            pOut += width;
+            pIn += image.getWidth();
+            pOut += getWidth();
         }
     }
     
@@ -519,7 +522,7 @@ int MicroBitImage::print(char c, int16_t x, int16_t y)
     MicroBitFont font = uBit.display.getFont();
     
     // Sanity check. Silently ignore anything out of bounds.
-    if (x >= width || y >= height || c < MICROBIT_FONT_ASCII_START || c > font.asciiEnd)
+    if (x >= getWidth() || y >= getHeight() || c < MICROBIT_FONT_ASCII_START || c > font.asciiEnd)
         return MICROBIT_INVALID_PARAMETER;
     
     // Paste.
@@ -539,8 +542,8 @@ int MicroBitImage::print(char c, int16_t x, int16_t y)
             // Update our X co-ord write position
             x1 = x+col;
             
-            if (x1 < width && y1 < height)
-                this->bitmap[y1*width+x1] = (v & (0x10 >> col)) ? 255 : 0;
+            if (x1 < getWidth() && y1 < getHeight())
+                this->getBitmap()[y1*getWidth()+x1] = (v & (0x10 >> col)) ? 255 : 0;
         }
     }  
 
@@ -563,24 +566,24 @@ int MicroBitImage::print(char c, int16_t x, int16_t y)
   */
 int MicroBitImage::shiftLeft(int16_t n)
 {
-    uint8_t *p = bitmap;
-    int pixels = width-n;
+    uint8_t *p = getBitmap();
+    int pixels = getWidth()-n;
     
     if (n <= 0 )
         return MICROBIT_INVALID_PARAMETER;
 
-    if(n >= width)
+    if(n >= getWidth())
     {
         clear();
         return MICROBIT_OK;
     }
     
-    for (int y = 0; y < height; y++)
+    for (int y = 0; y < getHeight(); y++)
     {
         // Copy, and blank fill the rightmost column.
         memcpy(p, p+n, pixels);
         memclr(p+pixels, n);
-        p += width;
+        p += getWidth();
     }        
 
     return MICROBIT_OK;
@@ -602,24 +605,24 @@ int MicroBitImage::shiftLeft(int16_t n)
   */
 int MicroBitImage::shiftRight(int16_t n)
 {
-    uint8_t *p = bitmap;
-    int pixels = width-n;
+    uint8_t *p = getBitmap();
+    int pixels = getWidth()-n;
     
     if (n <= 0)
         return MICROBIT_INVALID_PARAMETER;
 
-    if(n >= width)
+    if(n >= getWidth())
     {
         clear();
         return MICROBIT_OK;
     }
 
-    for (int y = 0; y < height; y++)
+    for (int y = 0; y < getHeight(); y++)
     {
         // Copy, and blank fill the leftmost column.
         memmove(p+n, p, pixels);
         memclr(p, n);
-        p += width;
+        p += getWidth();
     }        
 
     return MICROBIT_OK;
@@ -646,25 +649,25 @@ int MicroBitImage::shiftUp(int16_t n)
     if (n <= 0 )
         return MICROBIT_INVALID_PARAMETER;
 
-    if(n >= height)
+    if(n >= getHeight())
     {
         clear();
         return MICROBIT_OK;
     }
     
-    pOut = bitmap;
-    pIn = bitmap+width*n;
+    pOut = getBitmap();
+    pIn = getBitmap()+getWidth()*n;
     
-    for (int y = 0; y < height; y++)
+    for (int y = 0; y < getHeight(); y++)
     {
         // Copy, and blank fill the leftmost column.
-        if (y < height-n)
-            memcpy(pOut, pIn, width);
+        if (y < getHeight()-n)
+            memcpy(pOut, pIn, getWidth());
         else
-            memclr(pOut, width);
+            memclr(pOut, getWidth());
              
-        pIn += width;
-        pOut += width;
+        pIn += getWidth();
+        pOut += getWidth();
     }        
 
     return MICROBIT_OK;
@@ -691,63 +694,30 @@ int MicroBitImage::shiftDown(int16_t n)
     if (n <= 0 )
         return MICROBIT_INVALID_PARAMETER;
 
-    if(n >= height)
+    if(n >= getHeight())
     {
         clear();
         return MICROBIT_OK;
     }
     
-    pOut = bitmap + width*(height-1);
-    pIn = pOut - width*n;
+    pOut = getBitmap() + getWidth()*(getHeight()-1);
+    pIn = pOut - getWidth()*n;
     
-    for (int y = 0; y < height; y++)
+    for (int y = 0; y < getHeight(); y++)
     {
         // Copy, and blank fill the leftmost column.
-        if (y < height-n)
-            memcpy(pOut, pIn, width);
+        if (y < getHeight()-n)
+            memcpy(pOut, pIn, getWidth());
         else
-            memclr(pOut, width);
+            memclr(pOut, getWidth());
              
-        pIn -= width;
-        pOut -= width;
+        pIn -= getWidth();
+        pOut -= getWidth();
     }        
 
     return MICROBIT_OK;
 }
 
-/**
-  * Gets the width of this image.
-  *
-  * @return The width of this image.
-  * 
-  * Example:
-  * @code
-  * const uint8_t heart[] = { 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, }; // a cute heart
-  * MicroBitImage i(10,5,heart);
-  * i.getWidth(); //equals 10...
-  * @endcode
-  */
-int MicroBitImage::getWidth()
-{
-    return width;
-}   
-
-/**
-  * Gets the height of this image.
-  *
-  * @return The height of this image.
-  * 
-  * Example:
-  * @code
-  * const uint8_t heart[] = { 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, }; // a cute heart
-  * MicroBitImage i(10,5,heart);
-  * i.getHeight(); //equals 5...
-  * @endcode
-  */
-int MicroBitImage::getHeight()
-{
-    return height;
-}   
 
 /**
   * Converts the bitmap to a csv string.
@@ -762,14 +732,14 @@ int MicroBitImage::getHeight()
 ManagedString MicroBitImage::toString()
 {       
     //width including commans and \n * height
-    int stringSize = ((width * 2) * height);
+    int stringSize = getSize() * 2;
     
     //plus one for string terminator
     char parseBuffer[stringSize + 1];
     
     parseBuffer[stringSize] = '\0';
     
-    uint8_t *bitmapPtr = bitmap;
+    uint8_t *bitmapPtr = getBitmap();
     
     int parseIndex = 0;
     int widthCount = 0;
@@ -783,7 +753,7 @@ ManagedString MicroBitImage::toString()
         
         parseIndex++;
         
-        if(widthCount == width-1)
+        if(widthCount == getWidth()-1)
         {
             parseBuffer[parseIndex] = '\n';
             widthCount = 0;
@@ -821,17 +791,17 @@ MicroBitImage MicroBitImage::crop(int startx, int starty, int cropWidth, int cro
     int newWidth = startx + cropWidth;
     int newHeight = starty + cropHeight;
 
-    if (newWidth >= width || newWidth <=0)
-        newWidth = width;
+    if (newWidth >= getWidth() || newWidth <=0)
+        newWidth = getWidth();
         
-    if (newHeight >= height || newHeight <= 0)
-        newHeight = height;      
+    if (newHeight >= getHeight() || newHeight <= 0)
+        newHeight = getHeight();      
     
     //allocate our storage.
     uint8_t cropped[newWidth * newHeight];
     
     //calculate the pointer to where we want to begin cropping
-    uint8_t *copyPointer = bitmap + (width * starty) + startx; 
+    uint8_t *copyPointer = getBitmap() + (getWidth() * starty) + startx; 
     
     //get a reference to our storage
     uint8_t *pastePointer = cropped;
@@ -841,9 +811,27 @@ MicroBitImage MicroBitImage::crop(int startx, int starty, int cropWidth, int cro
     {
         memcpy(pastePointer, copyPointer, newWidth);
         
-        copyPointer += width;
+        copyPointer += getWidth();
         pastePointer += newHeight;
     }
     
     return MicroBitImage(newWidth, newHeight, cropped);  
 }
+
+/**
+  * Check if image is read-only (i.e., residing in flash).
+  */
+bool MicroBitImage::isReadOnly()
+{
+    return ptr->isReadOnly();
+}
+
+/**
+  * Create a copy of the image bitmap. Used particularly, when isReadOnly() is true.
+  *
+  * @return an instance of MicroBitImage which can be modified independently of the current instance
+  */
+MicroBitImage MicroBitImage::clone()
+{
+    return MicroBitImage(getWidth(), getHeight(), getBitmap());
+}
diff --git a/source/RefCounted.cpp b/source/RefCounted.cpp
new file mode 100644
index 0000000..3d4105e
--- /dev/null
+++ b/source/RefCounted.cpp
@@ -0,0 +1,46 @@
+#include "mbed.h"
+#include "MicroBit.h"
+
+void RefCounted::init()
+{
+    // Initialize to one reference (lowest bit set to 1)
+    refCount = 3;
+}
+
+static inline bool isReadOnlyInline(RefCounted *t)
+{
+    uint32_t refCount = t->refCount;
+
+    if (refCount == 0xffff)
+        return true; // object in flash
+
+    // Do some sanity checking while we're here
+    if (refCount == 1 ||        // object should have been deleted
+        (refCount & 1) == 0)    // refCount doesn't look right
+        uBit.panic(MICROBIT_HEAP_ERROR);
+
+    // Not read only
+    return false;
+}
+
+bool RefCounted::isReadOnly()
+{
+    return isReadOnlyInline(this);
+}
+
+void RefCounted::incr()
+{
+    if (!isReadOnlyInline(this))
+        refCount += 2;
+}
+
+void RefCounted::decr()
+{
+    if (isReadOnlyInline(this))
+        return;
+
+    refCount -= 2;
+    if (refCount == 1) {
+        free(this);
+    }
+}