What may look like to copies of the same digital painting alongside one another, is actually an ‘analogue’ stereoscopic 3D image. Cross your eyes and merge the two pictures to see it in action.
Digitally creating the paintings in a multi-layered photoshop document allows artist Theo Prins to then slightly adjust the angle and positioning of the picture and create the second view that merges with the former to create the 3D image when the viewer crosses their eyes and aligns them.
Take a look at more exampes on Theo’s website here.
There’s a much more coherent write-up here.
Prewarning: Puts a fair strain on your eyes first time you attempt it…