iPhoto file management

You can dump the originals when you've imported into iPhoto (by 'dump' I mean you can move them onto a CD/DVD or save them elsewhere).

iPhoto will keep the original file, plus a version that has edits and effects you have made. This is so you can always revert to the original if you want to. I'm not sure off the top of my head what the version in 'Data' is.

 

Any photos you add to iPhoto are copied into the originals folder and then never modified again. The data folder contains thumbnails of all of your photos for faster loading of the library, it does NOT have a full second copy of your photos. If, and only if, you modify a photo in iPhoto, it will save the modified version in the modified folder. This is so that you can always revert to the original.

Once they are in iPhoto, you can safely delete your folder of photos on the desktop. iPhoto should never, and will never, make more than two copies of your photos, usually it is closer to one copy unless you modify all of your photos from within iPhoto.