A. When you update your camera with CHDK, it doesn’t actually change the firmware. Because it is just a memory-resident program, it only remains in the camera’s memory until the camera is turned all the way off. So, if something goes wrong and camera does not respond, you can always switch the camera off (or remove the battery, and perhaps delete it from the memory card) to return to the original firmware. Recently, CHDK gained the ability to autoload (see the next answer).