If you have one of those digital camera’s that forgets what day it is after you’ve replaced the AA batteries you might end up with a lot of pictures with bad EXIF data tags.
As a geek and nitpicker I sort of dislike that. In fact, in Picasa all of those pictures ended up being cataloged in the year 2012 which is the default date of the camera apparently. Picasa I found out uses EXIF data and not the file date of your pictures. This makes sense of course. If you change a photo’s color settings for instance, the file date will change, the EXIF data won’t.
So to fix those bad dates I ran into this piece of software called EXIFViewer. The GUI look pretty damn old, but it works, so who cares. You can use it to set the EXIF date to a specific date and time, or perform a calculation on the selected files. For instance you can subtract 2015 days from all files, and whoosh those files back in time to when they where actually shot.
I also found some links to more EXIF data changing software is on Flickr. I haven’t tried any of these myself, but it might be worth a look. There’s a command line based tool in there as well, so if you want to do some scripting, that might be what you need.