If you cover the same people on a regular basis (city council, mayor, etc.) it's worth using the Faces feature. Faces lets you tag a face or multiple faces in a photo. Once you tag a face several times, iPhoto learns to recognize the face when you import new photos. This can be a great time saver, ensure that the correct spelling is applied to a person and will occasionally identify people in crowds that you miss.
First, select all the existing photos and drag them to the Trash in the Source list. Then hold down the Control Key and click on the Trash (or right click with a two-button mouse) and choose Empty Trash.
Import the Obama photos included in the sample files. Click on the Faces icon in the Source list and iPhoto will ask you if you want to assign identities to the images.
Edit the first one to read Barack Obama. As you begin to type in the second photo, iPhoto will suggest a match. Select Barack Obama on the first three photos then click the Continue to Faces button in the lower right corner.
This will take you to the main Faces section. Double-click on the photo of Barack Obama to look at the faces you identified.
At the bottom of the screen, you should see a message that states that Barack Obama may be in additional photos. Click on Confirm Additional Faces.
You now see a section of photos with unconfirmed faces.
Click to confirm the photos. You can also hold down the Option key to Reject a photo from a Faces group. Then click Done.
Click on the Photos in the Source List. Notice that a photo of Obama saluting is missing. Profile photos and obstructions like a hand or sunglasses make it harder for iPhoto to identify faces.
Double-click on the photo to edit it. Click the Info button on the bottom menu to open the tools panel.
When iPhoto can't attach a name to a Face, it will do one of two things: Place an unnamed face on the photo or leave the photo blank. If it adds an unnamed face, you can edit it like we did earlier. If it's blank, you can click Add a face and iPhoto will drop a box on the photo that you can move and adjust