I'm great at magic eyes / stereograms and have a ton of posters around my house with them, but I still had trouble with seeing the differences in the test images. I easily locked in my focus on the overlapping cat images but only one difference stood out to me. I eventually got them all but it wasn't that easy (maybe with practice I could get there). The differences are noticeable when I focus right on it, but when I'm looking at the whole image it's harder to tell what is missing from one eye.