Several operators are reporting that ISS is transmitting test images today (Oct 12) beginning about 1700 UTC. Two formats have been reported. Robot-36 (which is anticipated for most of Garriott's flight) and Martin-1. Several operators have uploaded these test images to the ARISS SSTV gallery. These test images will likely be removed to make way for the Garriott images when they begin coming down.
The following are examples of images received from the ISS (of Exp. 17 Commander, Sergei Volkov) by CT1EAT and N1JEZ.