Wow, that's something I had never considered. I did run into a bug with someone uploading a gif to our servers and our resize script spitting out a file per res

Wow, that's something I had never considered. I did run into a bug with someone uploading a gif to our servers and our resize script spitting out a file per resized gif frame (base_1.png, base_2.png, ...) that I had to fix but I'd never have thought of your example. We just took the first gif frame in our case, which would have been safe from this thankfully.