I love this visual oddity. We've seen this with craters on the moon and foot prints in the sand. The photographer has this to say about the photos.
"This is two copies of the exact same photo, rotated 180 degrees from each other.What do you think?
Are the letters on the marker raised or imprinted?
Is the marker itself slightly concave or slightly convex? "
Up or down?
Flickr Artist: mag3737
Tags: photos, optical_illusions, illusions, art