My first thought was that it must derive from the same source as “small potatoes”, i.e. referring to something of low value (because it is a cheap staple food).

Wiktionary supports this theory (see definition #3): https://en.wiktionary.org/wiki/potato

I’ve also heard “recorded on a toaster”, but that’s probably from the fact that a toaster is an electronic device, but much lower tech than a phone or camera.