Here is a great optical illusion photo taken of a Lufthansa 747-400 and a United 757-200 that were on simultaneous approaches to runways 28L and 28R at San Francisco (SFO).
The separation requirement for flying parallel and simultaneous approaches is 225 meters (about 750 feet).
These two aircraft are at a safe distance for the appro aches they are each flying. Due to the 747 being three times larger than the 757, and being slightly behind, it gives this incredible optical illusion.
Other nice illusions:
Charlie Chaplin Optic Illusion
Optical illusion - destroy your brain
How can be this be true? (Optical illusion)
Excellent pig illusion