So does the A above the E, indicating the crease in the cardboard. As someone that's written on cardboard quite a lot, it's pretty clear to me and isn't something I'd expect an image generator to accurately replicate, so to me, it's proof to its authenticity.

The cardboard is too perfect. It's like the ai is trying to make the text look like it was written over a piece of cardboard box at the fold, but there's no folds anywhere. Or texture, or gradient, or anything that would resemble a real piece of cardboard.