Parallelogram Optical Illusion

Which of two red lines in this image is longer?

See Another Random Optical Illusion

Scroll down for the answer and explanation.

Actually, they're the same length.

Explanation

Yes, they really are exactly the same length. We expect pictures to represent objects which are square or made up of right angles. In this optical illusion, the eye computes the distance as though both boxes were square, which would support the conclusion that the one line is shorter since its box is only half the size of the other.