On Wednesday, August 26, 2020 at 9:36:52 AM UTC-7, wrote:
I have an old Canon camera, model SD300, that I modified for taking
pictures in near IR and near UV. The largest capacity SD card it will
take is a 2GB.
...The cards have sat around for about a year and now most of the
pictures are corrupted.

Age causes the charge to leak, and any 2G card is probably a decade old.
Good news: you can get a format utility from the SDcard consortium

https://www.sdcard.org/downloads/formatter/

and if you choose the 'overwrite' option, it completely initializes all the bits
instead of just directory twiddling.

The complete rewrite takes a while, of course, but it does get rid of weak bits,
and presumably that's what aging has done.