Today, Google is honoring Eadweard J. Muybridge, the man who is most well known for capturing motion with the use of photography. He was born today in 1830 in England but spent most his days in the United States.
The imagery Google used in their logo was from one of his works where Leland Stanford hired Muybridge to see if all of the horses legs are on the ground when the horse runs. This was known as Stanford and the galloping question but helped us move into the motion picture stage of photography.
Here is the Google logo as a static image:
Of course, what would be a static Google logo in this case? Here it is animated:
For more on Eadweard Muybridge see his Wikipedia entry.