Your profile picture can also be called your avatar or Gravatar (globally recognized avatar), which is the small icon that appears next to your name. Generally, the same things apply to these icons as apply to artwork in general - make sure you are legally allowed to use the image or photograph before uploading it as your own. See the art theft and "Copyright Concerns" and follow accordingly for your profile picture. Anything that you have created that also falls under work and imagery allowed on this site, we welcome as your avatar.