Yes, if the physical storage medium they're living on develops a hardware fault.
http://alkiratech.tripod.com/j…..orruption/ has some examples of what image files look like when they're corrupted by hardware problems.
Make sure you have at least two copies of anything you want to keep, on separate media if you can. For example, you might have one on your computer's hard disk, one on a backup drive, one on a CD-ROM, one on a flash drive… None of them will be perfectly reliable, but overall you will reduce the chances of all your copies developing corruption at once.