First save the image to your SD card and then use the ACTION_SEND
Intent
.
http://developer.android.com/reference/android/content/Intent.html#ACTION_SEND
Intent share = new Intent(android.content.Intent.ACTION_SEND);
share.setType("image/*");
share.putExtra(Intent.EXTRA_STREAM, Uri.parse("file://" + pathToFile));
ctx.startActivity(Intent.createChooser(share, "Share image")); //edit text shown in dialog here