Any way to back to the original firmware?

Hi, from the FAQ:

Quote

Q. Does using the CHDK program void your warranty?

A. First, please bear in mind that CHDK comes with no warranty for any use; you use it at your own risk. What follows is just a few thoughts, and is not a legal opinion. Many believe that using the CHDK does not harm your warranty, since it is said to be loaded into the memory only temporarily (turn off the cam and it's gone completely) and that it leaves the original camera firmware untouched.
Canon Tech Support says: "Unfortunately, any upgrades to the software of the camera not performed by an authorized Canon Repair Facility, would void the warranty." ... and ... In further discussion with Canon about this specific hack, their response is: "If it is not Canon firmware the warranty would be void."

Is it an "upgrade" of the camera firmware when the firmware remains untouched? It's up to you to decide. Don't use it if you are not willing to take the slightest chance. Many many people have used CHDK on their cameras (including some very experimental versions) and there is no report of any permanent malfunction. Thus, CHDK appears to be quite safe to use as long as you make sure that it's the CHDK and not a real firmware update (A real firmware update which is not an official Canon update could alter or completely screw up the camera and will void the warranty). Addressing their second comment (i.e. "if it is not Canon firmware"): CHDK is NOT firmware. By very definition, FIRMware is software that remains in the memory of the device when it is not using any power-source.

However, this is not a legal opinion and the user accepts all risk of using it. And as a practical matter, if you send your camera in for warranty service, and Canon says your warranty is void because they found evidence of CHDK on your memory card, there is not much you can really do (what are you going to do? Spend thousands of dollars suing them to get your camera repaired?)

However, you can just wipe or remove the card.