I have always wondered if that pic was real or shopped I have caught many coconut crabs over the years and never anything nearly that size! If it is real that is one impressive crab. Its amazing how small they start off as. This crab I found dead in one of my traps. I dried him out and he preserved well. The smallest I have ever seen was about the size of a quarter.
Living in Guam in the late 1960's, Coconut Crabs were pretty abundant. The Chamarons (native Guam folk) would cut the top off of coconuts and set them on the beach, tied down. A crab would get it's claw inside and grab the "meat" and wouldn't let go, preventing it from removing it's claw. This made it much easier to grab.
My father was given a plaque with one stuffed and mounted on it where the crab was about 12 inches wide and 15 inches long.
I never saw one as big as the one pictured, but I did see them quite large.
They were excellent eating when caught fresh and boiled like lobster.