I just had the experience recently of trying to reset my Canon PowerShot SD750’s numbering back to the last picture I had saved. The little hack I discovered over the summer was that I could go into the menu, cycle File Numbering from Continuous to Auto Reset and back, and any file numbers I’d erased since the last saved picture were re-used. It worked great when I was carrying the whole summer’s worth of pictures on the card. With an empty one, though, it reset the numbering back to zero. I wanted my numbers back, so here’s how I did it.
I took the memory card out of the camera and put it into my computer’s card reader. I opened it in Windows Explorer (any file manager will do) and made a new folder named “100CANON” (the default photo folder name). I went into my photo library and found the latest picture I had taken, a file named “IMG1903.jpg”. I loaded it into the new folder and took out the card. I put it back into the camera, cycled the menu option to be safe, and took a picture. Voila! Picture 100-1903 was joined by number 100-1904. I deleted both (a copy of the one I loaded was still on the computer by default). Now the camera’s back to where it was.
I don’t expect this to be especially useful for a lot of people, but it should work on any Canon camera that uses the same file numbering (is that all of them?). It works because the camera, when numbering files, goes on either the last picture taken (on an empty memory card in Continuous mode) or the highest-numbered file on a non-empty card (in either mode). Copying a file you took with the camera, as far as I can tell, is crucial, because you cannot view photos that have been edited with a computer on the camera. Theoretically, the file could be copied and renamed to “IMG9999.jpg” and set the camera to start over, or “IMG7285.jpg” and set the next picture at 7286. Deceptive numbering like that isn’t very good for really determining how many photos you’ve taken with the camera, but it might be good for playing a prank on someone else’s.