Here's an illusion worthy of M.C. Escher. As the lines slant across the warehouse, one ducks behind the flagpole. Meanwhile, the flag seems to drape around the upper line. But if you Alt-arrow back to the previous pic, you'll see that the diagonal lines haven't moved at all; they're still firmly fixed within the camera.
These pictures have not been digitally altered. What you see is what came off the scanner. I will send prints to anybody for the price of reprints and postage. Write for details or better yet, keep your money and make your own pictures. I'm sure you can do a better job than I.