When you say agar.io, do you mean the type of game where orbs chase other orbs around and (basically) try and eat each other?
I can't see any reason why something like that wouldn't be possible personally. Try looking some of the example projects on real time multiplayer, then look at the file browser object for your photo functions.
Hope this can help with a place to start, good luck!
Regards,
Gideon.