On this very old, unused, real-photo card, we have what might qualify as an optical illusion.  Just looking at the card in your hand, along the lower left, there is obviously some kind of caption but it’s unreadable.  However when we scan the card, and enlarge the result, that caption springs into view and identifies the scene as Rio.  Even a magnifying glass doesn’t quite achieve that.  The reverse has some staining along the right edge.  Grade: 3