I tried crossing my eyes, but it’s not working for me; I keep seeing things blurry. Maybe I’m doing it wrong. However, I solved the first two puzzles. For the last one, I just guessed randomly. My guess wasn’t exactly correct, but it was close, just a little distance away.
One thing I noticed: because you're tricking your eyes into thinking they're observing at a different distance, your brain doesn't seem to correctly account for head tilt (my theory of the diagnosis). Anyway, I think you're head must be exactly level with the image or you'll get double-vision/blur
