Step 1: Locate the library
There are several ways to back up an iPhoto library. The simplest is to copy it directly to another drive or DVD. Go to your Home folder, then into the Pictures folder.
Step 2: Drag the library
The Library file is treated as a single folder so you can drag and drop it onto an external drive or onto a DVD and the whole thing will be duplicated byte for byte.
Step 3: Drag individual events
Instead of backing up the whole library, you may only want to back up events. Create a desktop folder, go to Events view in iPhoto, then drag events to the folder.
Step 4: Check the results
Open the folder you just dragged the images to and you should see that they have all been copied. Copy this folder to an external drive or to a DVD if you like.
Step 5: Export an event
Select one or more events (multiple-select by Shift + clicking) and choose File>Export. The Export window appears and shows the number of images selected.
Step 6: Choose quality
Select ‘Original’ in the Kind menu for exported images to be full-quality duplicates. To save smaller files, choose JPEG. Choose Export and a destination.
Step 7: Drag individual images
Double-click on an Event or go into Photos view to see individual images. Select pictures and drag them into a folder on the desktop, as you did for events.
Step 8: Export individual images
The Export trick works for selected images as well as Events. So if you want to change size or format of pictures during export, repeat the trick from step 6.