As you can see both pictures are the same, Why? because, the light that falls on their face, is positioned/coming from “their right side” thus the dark shadow of their nose falls both on their left cheeks.

Only the 2nd picture on the right has been “touched/photo shopped?”. How? Try this, Put the blue dot of the slider into the “close” level, their highest zoom.

Then, right click the picture and “zoom in” it, once or twice. Hold and drag/move it sideways left and right. Observe the differences of their eyeballs “shade” on both pictures, particularly on its “side corner”.

The “right side corner” of both eyeball of the girl in the first picture have a “lighter shade” because of the light that falls on it.

On the contrary, the “right side corner” of both eyeball of the girl in the second picture have “darker shade, hence, the “trick”

That’s what make the “illusion”, you just can’t tell the difference until you studied it carefully.