It disappears when the image is scaled (like many lemmy interfaces do). Make sure you look at the plain image without zooming.

I only started being able to see them a few months ago. Maybe the trick you haven’t heard is that , you know sometimes you can purposefully get double vision when you stare at the wrong distance ? try doing that when you look at the picture.

EDIT : https://www.magiceye.com/stwkdisp.htm

Try the one that says "wishing this for everyone", its really easy, it turns into an obvious peace symbol.