imgChild.buildDrawingCache();
Bitmap bmap = imgChild.getDrawingCache();
ByteArrayOutputStream stream = new ByteArrayOutputStream();
bmap.compress(Bitmap.CompressFormat.PNG, 100, stream);
byte[] byteFormat = stream.toByteArray();
String imgString = Base64.encodeToString(byteFormat, Base64.NO_WRAP);

<img src="data:image/png;base64,iVBORw0KGgoAAA....." />