I would love to hear what other projects have in place to prohibit AI contributions. If you don't have anything yet, feel free to use my text as a starting point. Thanks to @npub1zngf...fgsk for pointing out the missing license.
GNOME's default Image Viewer (Loupe) no longer accepts AI generated contributions. You can read more about the reasons for my decisions in my discourse post. I'm planning to adopt the same policy for the rest of the projects I maintain. And I think others should as well.