To get started, select a group of pictures in iPhoto. Under the Photos menu, choose Batch Change, or hit Command-Shift-B. When you do that, you’ll be presented with some drop-down options on how you’d like to modify the items. My favorite way to do this is by setting the title to “text” and then clicking the “Append a number to each photo” box. Which, as you might imagine, results in each photo being labeled with your custom title followed by ascending numbers. Neat, huh? If you prefer, you can also set a custom date or description.
So what? I dress my animals up. Don’t you judge me.
Modifying the metadata in this way is extremely helpful when you need to find a particular subset of photos (especially if they’re not grouped into the same event). You can also use this information to do all sorts of nifty tricks to impress your friends, such as creating Smart Albums (based on searching for the custom titles you created, for example) quickly. But only if you have friends who are easily impressed.
Creating Smart Albums (by choosing File > New > Smart Album) is a great way to search for all of the custom metadata you’ve added and organize similar photos together.