Try looking in your forum/includes/functions_gallery.php file for this:
Code:
Content visible to verified customers only.
And add this right below it:
Code:
Content visible to verified customers only.
That should take care of the image viewing permissions globally (showimage, ecards, print image, etc). The random/new images on your homepage would probably be a little more difficult though. You could just exclude those categories from that section though by looking in your index.php file for two instances of this code:
Code:
Content visible to verified customers only.
And replace each with this:
Code:
Content visible to verified customers only.