Sometimes one needs quick profile images in a development project. Enter Gravatar:
Your Gravatar is an image that follows you from site to site appearing beside your name when you do things like comment or post on a blog. Avatars help identify your posts on blogs and web forums, so why not on any site? source: http://en.gravatar.com/
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If you need a sample MD5 function, take a look at this repo.
You should spend some time getting to know what paramaters you can pass to Gravatar, such as size and default images here.