Attention to detail. The discerning eye will be able to pick up on the subtle changes that have been made to each image with Photoshop techniques. Clever thinking on the part of each artist.
Worth 1000 Subtle Changes has many more images here. Better than “Where’s Waldo?”
“On the Lam (or Zebra).”
Image courtesy of todmac
for the Subtle Changes 5 contest via http://www.worth1000.com/cache/gallery/contestcache.asp?contest_id=1723&display=photoshop.
“ScubaDiver.”
Image courtesy of DaemonDCLXVI
for the Subtle Changes 11 contest via http://www.worth1000.com/cache/gallery/contestcache.asp?contest_id=23672&display=photoshop.
“Lettuce.”
Image courtesy of monkeywithnobrain
for the Subtle Changes 7 contest via http://www.worth1000.com/cache/gallery/contestcache.asp?contest_id=4744&display=photoshop.
Need help?
- Look at the prisoners top center.
- Look at the diver’s back.
- Look what is peeking out top left.
See:
Quipster 
Wow, I must be good at seeing the little things because I picked up all three before I saw the answers. Must be my keen eyes that help me find the good stuff on the clearance racks. 😉
Good eye comes from years of experience and life in dealing with kids and family. And yes, scanning across the department and other stores for the buys of the century!