Gravatar

A very easy way to add user profile pictures is by using 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?

Basically it assigns a picture with your email address. Just log in to - https://en.gravatar.com// to upload one.