This is a microtask for Outreachy applicants for {T158909}.
* Set up local development environment. (You'll probably want to use [[https://www.mediawiki.org/wiki/MediaWiki-Vagrant|MediaWiki-Vagrant]])
* Set up [[https://www.mediawiki.org/wiki/Extension:EventLogging|EventLogging]].
* [[https://www.mediawiki.org/wiki/Extension:EventLogging/Guide#Creating_a_schema|Create an EventLogging schema]] (on your own machine, not meta.wikimedia.org! see [[https://www.mediawiki.org/wiki/Extension:EventLogging#Installation|docs]]) for data to be collected for the captcha. (Doesn't have to be realistic, just put in some fields.)
* [[https://www.mediawiki.org/wiki/Extension:EventLogging/Programming#How_it_works|Make MediaWiki log some data on registration.]] For example, you could use the [[https://www.mediawiki.org/wiki/Manual:Hooks/LocalUserCreated|LocalUserCreated]] hook and record the IP of the user.
* Submit the code you wrote to [[https://www.mediawiki.org/wiki/Gerrit/Getting_started|Gerrit]]. Make sure to start the commit message with `[DO NOT MERGE]` and explain in the commit description that this is an Outreachy microtask and not intended to be merged. (Eventually the code should go into a new extension, but setting that up is too much work for a microtask.) Add mentors as reviewers.
Please don't hesitate to ask questions if something is not clear. The documentation for EventLogging is particularly horrible :( Don't spend too much time trying to understand it, just ask. [[https://webchat.freenode.net/?channels=#wikimedia-devrell|#wikimedia-devrel]] or {Z610} is a good starting point.