Is it an idea to define a starting point image? So that would be the first one would see when starting the app.. (I could insert an image then with something like: "Hi, you are entering the Gallery of <insert> , enjoy your stay!")
Clickable images with possebility for hyperlink to external pages
If that is do-able then a main hallway with entrances to user galleries should be do-able also..
One step further, a customisable avatar (something like IMVU or 2d life)
Add a chatbox and.. okay, okay.. I'll stop now..
Charley