A collection of nearly 10,000 real profile pictures for use as samples avatars in UI mockups. All of the uiFaces avatars come from real Twitter users who have given permission for their face to be used in mockups. There is also an authorised section that includes people who are happy for their avatar to be used on live products as well. For those that what to automate finding avatars even more, there is also an API that you can use to fetch random or specified usernames in JSON.