Moving pictures. You might like to view this full-screen.

These are animated classical paintings by Rino Stefano Tagliafierro - who calls them "a tribute to the art and her disarming beauty."  Rino used layered animation, processing each still photo in Photoshop, then separating different elements on their own layers—parts of the background, elements of the figures, and so on. 

These still layers were then imported to to After Effects, where they were animated in layers, moving them at sightly different speeds to achieve a parallax effect; since objects closer to the viewer appear to move faster than objects far away, this makes your brain think the camera is moving in three-dimensional space. It's the same parallax effect used in old video games, when true 3D was still not available. 

Te creators then applied some subtle deformation to particular elements of the image (like the wings of the owl) to give the illusion of actual movement.