@AnnieC @MarkHoltom I think there are very good reasons to believe that this is real. What is most convincing, I believe, is the low quality of the photograph. AI tends to generate images that have high sharpness, have strong lighting and tend to be weirdly wrong in some ways. Here — the lighting is very realistic, which is to say, not very good. The image it totally out of focus (focus point seems to be around the back of the seat on the right side. McCartney looks old, tired and very human, by no means fancy as AI would probably depict him. The picture is shot using wide angle, which gives a distortion that often AI does not do quite naturally. The reflections in the window look reasonable.

But more importantly: The photo is 9 years old and thus predates the era of AI fake images: https://www.dailymail.com/tvshowbiz/article-4650398/Sir-Paul-McCartney-75-spotted-casual-train-ride.html