Did you know that when you add an image to iPhoto, by default it’s actually copied into your iPhoto Library? Let’s say you download an image from the internet to a folder on you Mac. Later you want to add the image to iPhoto, so you drag the image from the folder and into iPhoto. You now have two identical copies of the image – the one in the folder on your desktop, and the one in iPhoto. If you delete the image from your Mac’s desktop, it will still exist in iPhoto.
Many people keep a copy of the images they download (or have emailed to them), even after adding (and copying) the images to iPhoto. Over time, these copies can gobble up hard drive space.
Thus, it’s typically best to delete images after they are imported into iPhoto. Of course, don’t forget to backup iPhoto (or your Mac) often.
What if you don’t want to copy the images into the iPhoto library? In iPhoto 6 preferences, there is an option to deselect “Copy files to iPhoto Library folder when adding to library.” If you deselect this, images will NOT be copied into iPhoto. In most cases, I don’t recommend this. I prefer to have all images copied into my iPhoto library, where they can easily be titled, duplicated, keywords can be added, etc. Also, it’s easy to back up iPhoto.
Note that iTunes works in a similar manner – by default, when you add a song, video, music loop, podcast, album art or even a PDF, it’s actually copied into the iTunes library. Also like iPhoto, there’s an option in iTunes preferences to “Copy files to iTunes Library folder when adding to library.” If you deselect this option, iTunes will play back music or videos without copying them into the iTunes library folder. The disadvantage to this is that you might erase the original file, causing a broken link in iTunes. Also, it’s easier to backup your iTunes music when it’s stored in one single folder – in this case, the iTunes library folder.
iMovie and Garageband are a little different. When you add data to these applications – a video clip or photo in iMovie, a drum loop or instrumental track in Garageband – that data is copied into the project file. There is no option to deselect to get around this. That’s part of the reason Garageband and iMovie projects can quickly get huge, in terms of gigabyte size. On the other hand, these projects are easy to back up, because all the data is stored in one place.