Maybe you should show these files via a script? Write a small php script to do the following and just use that, in combination with .htaccess, to not allow direct access.
PHP Code:
//something like..
header("Content-type: image/gif");
readfile("/path/to/image.gif");
exit(0);
then set your .htaccess to redirect on anything that is not an image OR store the images outside of public view.