This is done by taking a still image, cutting out the people/objects, then offsetting them from the background and each other in Z space, and moving a 3D camera around/among them. They can be made to seem to move by using the puppet pin tool to distort the image. It is tricky to do well, but not that complicated in theory. (Like most things.)
Google "2.5D after effects tutorial" or something like that to see lots of examples of how to achieve it.