iPhoto '09 Faces
Without question, the snazziest addition is Faces, iPhoto's face-recognition technology. As you add a photo to your library, it is scanned for areas that resemble faces. If it finds a face (or more than one), iPhoto then tries to match it to the characteristics - shape, eyes, mouth, nose and more - of similar faces in other photos in your library.
You need to put in some work when you first start using the feature, running through quite a few photos in your library and identifying them appropriately (also known as "tagging"), by clicking on the Name icon at the bottom of the screen, adding their nickname, full name and email address to their Face record (iPhoto doesn't link with Apple's Address Book, which would be useful for filling out the additional information).
When you are browsing photos and click on the Name icon in the toolbar, iPhoto will ask you if a recognised face belongs to someone you've already identified in your Faces database.
If you run into a photo that contains a face, but iPhoto for some reason didn't recognize it - parts of the face might be obscured, for example - you can tag it using the "Add Missing Face" button. This process solely lets you associate the photo with a given individual; for various reasons, iPhoto doesn't incorporate that selection into the face-recognition algorithms.
Once you've got a representative set of names, clicking on the Faces section in the Library panel lets you associate more of your photos with people you have added to your library. The program displays a corkboard-style background, with an icon for every person in your Faces database; double-clicking on an entry shows you all the photos that contain that person, as well as a list of pictures that iPhoto believes might contain them as well.
If you click the Confirm Name icon at the bottom of the screen, each of the thumbnails zoom to the face in question, and clicking on it once accepts the suggestion, while double-clicking on it rejects it.
There are shortcuts you can use when accepting or rejecting faces in Confirm Name screen: holding down the Option key will reject the photo if you click on it, and, if you have a whole group of photos where the person is correct, just dragging a marquee around the group will automatically accept them (Option works here, too).
And, before you click the Confirm Name icon, if you know a photo in the suggested list contains someone else, double-clicking on it previews the photo, where you can change the name to the correct individual. With all the necessary clicks, it's not the most fluid interface, but it works.
It's important to set some realistic expectations with Faces. This is not like the sexy face-recognition stuff you see on TV shows, where everyone is discovered immediately and appropriately. iPhoto frankly missed a lot of faces, and even on occasion thought inanimate objects were faces. And, despite the claims of some pet lovers on the web, iPhoto never recognised our cats or horse, even when we tried to force the issue.
You also have to work at it as you go. iPhoto doesn't make any assumptions, even as your library grows, that a new photo contains your dad or your uncle Joe: you need to use the Name button or the Faces window when browsing new pictures, to verify and clarify.
As we gradually added thousands of photos to our library over the course of a few days (ultimately surpassing 10,000 photos), iPhoto got increasingly better at recognising the most important people in the pictures, which makes sense, since there were more pictures of those people in the library. Apart from the odd pairings [I guess my dad does kind of look like Chairman Mao] we're fairly impressed with what Apple's been able to do here.
As you begin to add more photos of your friends and family to iPhoto '09, the chances of a good match increase. In this screen we can click on each individual picture to confirm, but since they're all correct matches, we can drag a marquee around all of the images to confirm them and click on the Done button at the bottom of the screen.
One nice tip regarding Faces: you can drag multiple faces to the Album section of the Source List, and iPhoto creates a Smart Album that includes all of the people you selected. You can then edit that album to further refine the selection criteria ("only those photos that contain Joe and Sue," for example), and as you tag new photos with those people, iPhoto will add the photos to the album.