Kant: "The Universe Has a Beginning is False"

[Veritas Aequitas]

Isn't the face of Einstein an illusion?

Not in this case.

The illusion is seeing/perceiving and realizing a convex-3D face of Einstein when what is presented is a concave-hollow mask.

You have to observe the experiment in the link.
https://www.youtube.com/watch?v=BaofyuCXZ_0
Click the link and follow the experiment.

In a normal mask, there is the convex-3D side and thus the other side is concave and hollow.
But when the mask is turned to the hollow side, what is perceived is always a convex-3D mask.
In this case whenever the mask is turned continuously the person cannot see the hollow side of the mask but what is always perceived is a convex 3D mask of Einstein.

There is no concave or convex things there. It is flat. Your computer screen.

OK, the picture was from a flat computer screen but is a record of a mask with two sides, one concave-hollow and the other convex-3D.
The experiment is with reference to 3D objects not 2D objects.

https://www.youtube.com/watch?v=BaofyuCXZ_0
In that experiment, the observers always perceived a convex 3D mask of Einstein even when the concave [hollow] is presented to them.

Here is another;
https://www.youtube.com/watch?v=ORoTCBrCKIQ&t=1s

The control is if one were to view an apple in the same situation, all will perceive the hollow side and the convex side.
This experiment of emergent only take effect with human faces.