If you are using a small screen device, you will spot it immediately. But it might take awhile for bigger screens. Basically, for me, if I look very closely at the picture, I won't see anything. However, from a certain distance, I can see it's a panda. Therefore, I just want to keep this picture as a reminder for me: "I need to look at subjects from all angles of direction and all distances to understand this universe more".
PS: here is the explanation from the website:
If you look very closely at the lines (which can be a little disconcerting) you may notice tiny imperfections in the zig zags. Near the edges of the panda, the otherwise ruler-straight edges of the zig-zag lines are offset by just a tiny amount. Sometimes as little as a single "pixel" (the smallest possible size that can be presented on a computer screen). To a casual observer, this is nearly imperceptible. Indeed many will go by this image not seeing the hidden panda at all. But if you are observing it from the right angle, and at the right distance, those tiny offset pixels inform your brain that something more is at play.
Once your brain figures out that the pattern isn't perfect, it will darken your perception of certain regions, which unveil the hidden panda.
