If you’re even a moderately heavy photographer, you may find that your iPhoto library is actually much larger on disk than it is reported in iPhoto. Confused why this is?
The answer is simple: there is a lot more to your iPhoto Library package than meets the eye. Control- (right-) click on it and choose Show Package Contents. When you do you’ll find that it holds a wealth of items not counted within the iPhoto application but that consume quite a bit of space.
For example, my 98GB iPhoto Library contains an iPod Photo Cache folder that weighs in at just over 20GB. A Modified folder houses 15.4GB of data. And the Originals folder holds over 59GB of stuff. So, as London’s constabulary is so fond of saying, what’s all this then?
When you sync photos to an iPod or iPhone, iTunes creates this iPod Photo Cache folder and places in it the scaled images that are synced with your iPod or iPhone. Each file is 1.5MB. If you sync a lot of photos, over time this folder is going to be mighty bulky, as it is in my case. If you toss it out, iTunes will recreate it.
That doesn’t mean tossing it isn’t a good idea, however. That 20GB iPod Photo Cache folder of mine likely has images in it that I have no desire to ever place on an iPod or iPhone again. Chucking the folder gives me a fresh start (though it will take longer to sync the iPod or iPhone when I next want to add photos to one of these devices because iTunes will once again have to create the converted images).
As for the Modified folder, when you edit an image with iPhoto, it keeps the original in an untouched state and creates a modified copy. That’s why you can select an edited image and choose Photos -> Revert to Original (or Reprocess RAW, if you’re working with a RAW file). These copies appear in the Modified folder.
And I don’t think I need to explain what the Originals folder is for.