Use Intent.ACTION_SEND to hand the image off to another program.
File F = new File("/path/to/your/file.png");
Uri U = Uri.fromFile(F);
Intent i = new Intent(Intent.ACTION_SEND);
i.setType("image/png");
i.putExtra(Intent.EXTRA_STREAM, U);
startActivity(Intent.createChooser(i,"Email:"));
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