if you know the software, all you have todo is guess the name of the pictures, and it looks like they are re-named numerically, so it's easy.
try it, Login, right click the picture, select open image in new tab, it should take you to a page that is just the picture on a blank screen, copy the url.
Sign out, paste the url and it will show you the same page.
Which means the photo directory is not protected by the global privacy settings.
It's happening to the new (last few days) upgrade as well as the old plugin.
Running 1.5.1 on two sites.
I need to fix this quite urgently, any suggestions.