When a new user joins the site a profile picture is automatically generated for them, how is this image generated? And does SE do it, or a third-party application?

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They're third party. Look at the src URL of one. Here's muru's:


The jumble there is an MD5 hash of the user's email (failing back to network ID if no email set).

This can be overridden by the profile image. These are uploaded to Imgur (like other images here are) and takes preference if set.

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    What a happy coincidence that muru was the person to post the other answer. – Oli Sep 16 '15 at 13:06
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    Nooooooo! My secret identity has been brought to light. :P – muru Sep 16 '15 at 13:06
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    A lot of mythology (especially related to natural magic) holds that knowing the true name of something gives you ultimate power over it... What they didn't know at the time is that something's true name is actually just the MD5 of their main email address. That's why I have so many upboats. (Ps I use a fake email account for my Gravatar! Bwahahaha!) – Oli Sep 16 '15 at 13:14
  • And if they set their own image, then does the gravatar one get deleted, or stay? – user364819 Sep 16 '15 at 13:15
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    You're asking questions that are super-easy to find out on your own ;) Right click an image, copy image location. – Oli Sep 16 '15 at 13:16
  • @Oli: upboats? – user364819 Sep 16 '15 at 13:16
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    All the upboats. – Oli Sep 16 '15 at 13:16
  • @Oli: one day I shall reverse the MD5 hash of your email address and the truth will be known about your identity! – Nathan Osman Sep 17 '15 at 3:24

Third party. The service is by Gravatar, which provides similar services for a number of sites, including Github, Disqus and Wordpress.

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    Not that it affects your answer in any way but... the owners of Wordpress bought Gravatar in 2007. Wordpress and Gravatar had been pretty heavily interlinked for a long time before then and they did the right thing™ for a service they were sucking many gigabits of bandwidth from. – Oli Sep 16 '15 at 13:09
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    then they had to force current gravatar users to "receive" a non deletable wordpress account... – Mateo Sep 16 '15 at 14:00

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