I don't think you get the point he's trying to make. No one is claiming the pic is their own. The pic is used to illustrate your points. For example, if I made a video about how I don't like Joker's new look in Suicide Squad and the video is literally just me talking and trying my best to describe it without a pic or thumbnail or anything, you'd still have no idea what I'm talking about. Sure, you can see an ad on tv or google the image I'm talking about, but if you have to seek information elsewhere to understand what I'm talking about in my own video, then I failed in the point I'm trying to make. Just imagine doing some sort of presentation at school or a board meeting without any slides, bullet points, bar graphs, nothing. No visual aids at all. Sure it can be done, but visual aids help you and helps maintain crowd interest.
Look at the bigger picture. Can you imagine AVGN, Nostalgia Critic, Cinema Sins, Honest Trailers and so forth.... just being a guy sitting in a room talking? You need to see at least footage of what they're talking about/poking fun of to get the full context.