I'm not talking about dirty politics here, but rather compression of the file, lossy compression in specific - the type that creates smaller file sizes for jpegs and what not. Lossless Tiff formats keep all the pixels, which mean the image quality won't suffer over time. One thing I learned long ago about jpegs is that every time you re-save one it compresses it a little more, if you do this a lot over the course of years it will definitely lose a lot of image quality.
2. Unrecognized file format
Ever find an old file on your computer that you can't seem to find any application that will open it? Proprietary file formats might offer great features today but there's a chance they'll not be supportable in the future. One way to sustain images saved in proprietary file formats is to have a good migration plan in place. Meaning if you have a bundle of files that only application X can open, you should routinely make sure that application X still works and that the files can still be opened. Other times to think about if you have to migrate or change files are when you upgrade an operating system, when a new version of application X comes out, and upgrades in general.
Without a good system in place to know where a specific digital image (or file) resides it often becomes unfindable, especially as more and more images (or files) are stored in the same context. One method of insuring that you'll not accidentally delete, destroy or lose a certain file is redundant storage. Basically keeping copies in multiple places. If you're dealing with large file sizes this might be restrictive, but storage costs are getting cheaper all the time. I just saw that you can buy a 1 terrabyte external hard drive for less than $300 these days. Of course if you put all your data there, and only there, there is a chance that in one terrible second something happens and it all disappears, like say a fire or flood. In order to prevent something along those lines many smart archives keep a copy of the important things off site, and some even in cold storage.