The best solution is to make a few small changes to your library to help keep everything organised more neatly. You can merge events or albums together to lessen the number shown in the main window, and renaming photos can not only help when looking for particular images, it can also help when uploading the shots to sites like Facebook and Flickr.
Choose an event from the sidebar on the left and open it up. Select all
the photos using the Edit menu, then click Photos in the menubar andselect Batch Change from the list that drops down.
You can rename the photos you have selected to a title that memorably describes the event with a number added at the end. The number will allow you to find them quickly at a later date.
Now drag one event onto another to merge them together. The fewer events that are visible, the cleaner iPhoto looks. Don’t worry, you’ll still be able to find photos thanks to their new names.
The Key Photo is the photo that shows when you’re in the process of viewing all events. Roll your mouse over the event until you find one you like, then hit the Spacebar to select it as a Key Photo.