Funny that you ask about this, I was considering an effort to make a new set of avatar images to pick from that are Ibotta-made but if everyone is ok with these then that works too.
That weird default one a lot of people have where it's a window or something, I'll be removing that one soon and replacing it with a custom one. Hopefully on Monday!
If you truly want to encourage individual avatars, just leave the window one as the only avatar. People will find a way out how to change it, just to make themselves stand out.