No, I am thinking through this properly, you're just being overly paranoid. A computer ML system right now will not be able to, with a high degree of accuracy,

No, I am thinking through this properly, you're just being overly paranoid. A computer ML system right now will not be able to, with a high degree of accuracy, know enough about the image to provide targeted advertisements. They even showed samples of descriptions; they're vague and general, not specific. The description might be "two people, outdoors, at beach" while the content could be "Awesome beach day today with my best buddy!" with X tagged in the image, geolocated to "Y beach" (either through your phone/camera's geolocation feature, or the poster specifically tagging a location which is something Facebook encourages), posted at Z time. Which do you honestly believe is going to provide more information for targeting? Hell, even if the content is "It's a beautiful day out!", you'd still have far more information from the metadata (tags, location, time) than the vague description the auto-generator could possibly provide.