This is just the alt-text associated with the image and is there for accessibility purposes. That text is always part of the page even without the "glitch". This to me is a good use of AI as it provides a richer experience for those who can't otherwise view the images.

I suppose it might make some people aware, who weren't otherwise, that their images are being processed for content.

Much more interesting and readily available though are the "interests" Facebook assigns to you, which everyone can access: Settings | Ads | Your Interests. These hint at much deeper analysis that is being done with data, and data from other sources beyond just analyzing pictures for content.

This is the golden goose from Facebook's perspective. Their whole business is based around having a giant ontology of subjects and slotting you into this giant graph, then selling access into that ontology.

That has been the basis of targeted advertising since well-before the advent of the internet, but now the ontology is much, much richer and the people are providing the data used for the AI-driven slotting all on their own.