Your profile allows you to use an avatar and/or a picture if it falls into a certain format. It can only be 100x100 pixels and the filesize is limited also. There's a pretty good selection already available here. I uploaded my own picture but it can only be seen in with my profile information as it exceeds the 100x100 pixel limit. You can try modifying your own or just use one that's already available here.

Good luck!