So if the idea is to keep existing functionality "functional", you might consider: rather than having a bunch of zero-length jpeg files (which might create a bad "edge condition" for some applications), you could unlink the existing file and replace it with a symbolic link (same file name) pointing to some known and suitable image (in an ms-windows file system, the term would presumably be "short cut", but it's the thing created by the perl "symlink" function).

IOW, instead of having a (few) million distinct jpeg files that you don't need, you have that many symlinks to a single image file. You could even have some fun with that... you know, kittens and/or puppies and/or infants, or maybe a mushroom cloud or one of those "sculptures" consisting of part of a car sticking out of the ground... Something that could give the viewers a chuckle in the context of reviewing a car insurance claim. (Oh wait, do insurance agents have a sense of humor?)