- Hold down the Option key and click on the Create button on the bottom right of the iPhoto window.
- From the pop over panel, select Smart Album.
- Name the Smart Album something like "unnamed faces".
- Set the criteria to read "Face - is - unnamed.
To work your way through the unnamed photos:
- Double click the first photo shown and click the Info icon on the bottom toolbar.
- The Faces section of the Info pane will show how many unnamed faces there are in the photo. (If you just see the word Faces, click on it to open the Faces section.)
- Name the unnamed people in the photo by clicking on the word "unnamed" under the face and typing in their name. If there are faces in the photo that iPhoto doesn't recognize as a face, click Add a face... in the Faces section of the Info pane.
NOTE: This Smart Album works in iPhoto '11, but in iPhoto '09 it can be somewhat flakey and miss some unnamed faces.