Research has shown that any picture in which the subject is looking directly ahead will have eyes that appear to look at you no matter the angle from which it is viewed. This is because pictures are 2D representations of a 3D world. As such, our brains ignore the clues that remind it that we are looking at a flat object and focus instead on the dimensional illusion created by the representation of light in the picture. No matter the angle from which we see it, even if it is a very skewed view from the side, we'll perceive it as a cohesive picture oriented toward us.
The alteration I'm describing adds an actual 3D effect to the picture which is not consistent with the cohesive view, making it disturbing and, thus, creepier than a static picture with eyes that look directly forward. It works by receding the eyes below the surface of the picture. The depth of the eyes allows the edges of the eye sockets (which are not receded) to hide the whites on the side it is being viewed from, just as would happen if an actual person was turning their eyes toward you.
Step 1: Gathering the Stuff
a graphic file of your picture of a subject looking straight ahead
OR two prints of the same subject that are the same size and resolution
poster board or card stock
a sharp craft knife
markers or colored pencils
frame with or without mat - the effect is easier to see without the frame's glass