A reader who prefers the anonymous life, noticed a discrepancy between iPhoto and the Finder. He wrote:
I have a MacBook Pro that is a couple of years old and recently, to clear up some much needed space, I went through and (after backing up my pictures) deleted about half of my photos. I gained a lot of space but I then noticed that iPhoto tells me that I have just under two-and-a-half gigabytes of photo yet when I select the iPhoto Library file inside my Pictures folder and press Command-I to bring up the Info window, I see the file is several gigabytes larger. Where are those extra gigabytes coming from?
It’s useful to know what you’re looking at when you examine each number. When you’re in iPhoto and select Events or Photos, the Information pane at the bottom of the window displays, among other things, a Size entry. The number here indicates the accumulated storage consumed by the original photos. So, if you were to export all the photos in their native format and resolution, the resulting folder full of the things would be approximately that size.
Now biff on over to the iPhoto Library item in your Photos folder, Control-click on it, and choose Show Package Contents. Inside you’ll find a load of items including Modified and Originals folders as well as thumbnail database and metadata files. Those other items take a fair amount of space too. That Modified folder, in particular, could be eating up huge amounts of storage because, within it, are images that you’ve edited. (This whole Originals/Modified scheme is what allows you to revert edited images to their original state by choosing Photos -> Revert to Original.)
There’s very little you can do about the contents of the iPhoto Library package, but there is something you can do in iPhoto. Control-click on the Trash icon in iPhoto’s Library list and choose Empty Trash. This deletes all the images you thought had been deleted (but hadn’t been because you didn’t realize that you need to invoke this Empty Trash command to really get rid of them).