The World's Most Difficult Puzzles are Double Sided. It has the same photo on each side, offset 90 degrees from each other. View a sample! Having the same picture on both sides makes any puzzle hard, but there's more to the story. Jigsaw puzzles are cut in a press, stamped out like dough cut with a cookie cutter. This makes a groove in the top of the puzzle and leaves the bottom flat. Any savvy puzzler would easily pick up on this and be able to tell immediately which side is which, except that the puzzle manufacturer cuts "The World's Most Difficult" puzzles once from EACH side, cutting the vertical locks from the front, then flipping the puzzle over and cutting the horizontal locks from the back. There is no way to tell which side is which! Each piece must be compared on both sides for size, shape, color, and fit. This is very important. If the pieces don't fit perfectly, you've got it wrong. You'll see what we're talking about when you try to put a "World's Most Difficult" puzzle together. It's Very Challenging!