My guess is that it is a jpg but I'm not a techy.

On the version I saw in Facebook, the red ball was rotating in the opposite direction. I couldn’t mimic it here.

What caught my eye is that the light/shadow pattern inside the hexagons changes, like the light is coming from two different directuons.

it looks like the purple middle column is drifting behind the red ball. And the illusion doesn't work if you cover up the red ball with your hand ))

I'm guessing not everyone sees it!

I see it now. Thx.

I like these illusions, it points out just how our vision system is seriously broken. Intelligent design... yeah right

You might enjoy this collection, http://www.ritsumei.ac.jp/~akitaoka/index-e.html

A classic sample still image that appears to move:

It seems to have some relation to focus. It only moves if my focus shifts, even the slightest bit. Pretty much stops if I stare at one spot.