I guess it's time for bed for me, if something this random popped into my head. I get the @ system, and I know there's a block user option. So, say if someone I had blocked were to @ me, would I be notified?
You could do it visually. As you said, search and see what comes up without an image in the results. Or, do an advanced search to list all games for a platform and see which don't have a pic. There are likely 10s of 1000s of them. Also, you end up with a lot of oddball listings that may be better off without an image.