Picture attribution is a feature that causes the name and avatar of a user who uploaded an image to appear in captions when the image is used in thumbnails.
The name of the uploader also appears in search results, so it may lead to people reaching pages because a name of the user targeted that page as relevant to the search terms, causing some sort of confusion.
Note: This feature has been discontinued on Wikia, so it shouldn't be necessary to disable it anymore!
How to disable it
You can request Staff to disable it entirely from your wiki sending a petition from Special:Contact on your wiki. This will remove the code entirely from the pages.
Note: The class name of the element was
picture-attribution before the changes made on May 6th
Keep in mind that if you hide it by CSS, the HTML code generated is still there, and thus the search results problem.