I think you are talking about scratches to the film stock? Film is pretty prone to scratching, it can get scratched from handling and from being run through the projector, from pieces of grit and such. That makes those weird hairs and lines when you watch them. Sometimes when films (and photographs, when you're working off the negative) are digitized they will remove these with retouching algorithms, or by hand. There's an algorithm built into Adobe Photoshop, and built into settings in scanning software paired with high-end machines. When I digitize images (I'm an archivist) I usually do not use them for preservation scans, but they can make a nicer image for print purposes, and I'll occasionally advise people using our historic images that there are options to make the images look a little less like rats have been gnawing on them.

There's some interesting research into the algorithms for touching up film and photos, if you're curious. This is an interesting overview with math equations and other excitement. Of course then people go in the other direction and add them to new stuff as well! :P