I finally decided to blog about the little hack I discovered over the summer. My Canon PowerShot SD750 (and all other Canon cameras, as far as I know) numbers files by user preference, either continuously or resetting on each new folder and blank card. I found a way to hack this setting so experimental pictures you don’t want to count in your photo total can be re-used. This only works on deleted photos right after your last kept one, so it won’t reuse other unused numbers in the sequence.
For example, you keep picture 1343, then take five test pictures and delete them all (1344-1348). By going into the menu, selecting the File Numbering option, and cycling the setting from Continuous to Auto Reset and back, you can make the camera re-use those five numbers. If you previously deleted picture 1245, though, it still stays unused.
This is a good short-term hack, but it can’t be used retroactively. You have to do it before you save another picture. If you forget and save picture 1349, in our example, you’ll have a five-number gap, and you can’t fix that unless you delete photo 1349, as well.
I also discovered a way to get back your numbering if you accidentally reset it by performing this hack on an empty memory card.