Is this figure spinning clockwise or counter-clockwise?
(Image: Nobuyuki Kayahara/Wikimedia Commons)

This image shows a female dancer pirouetting in a continuous loop. The illusion has to do with the direction in which she is spinning. Viewers will initially think that she is turning in either a clockwise or
counterclockwise direction. However, when observing the image at other times, the same viewer may feel absolutely certain that the dancer is spinning in the opposite direction. In reality, this animation is on a continuous loop and does not suddenly change directions.
Why is it impossible to define the direction of the spin? This optical
illusion tricks you with depth perception.

Because there aren’t enough clues about the depth of the dancer image, no one can define the direction of her spin with absolute certainty.

The image is a silhouette, so the dancer’s pony tail or extended arm
can only be seen when she’s facing to the side. They disappear from
view at the critical moment when we need them to provide information about depth and direction.