This is true for many airplanes. The first time I saw the SR-71 I was shocked at how large it was. The photographs simply don't do them justice and often the pics that are used are those of the planes flying which have no items to set a scale with.
For those wondwring, the Blackbird is the same lenght as a 737-600. So, the next time you board a 737, try to picture something that size going mach 3+...