How Do I Crop A Photo On A Mac?
If you have a loose photo, the easiest method is to open the photo with the Preview application. Drag to the select that area that you would like to crop it to and then go to Tools > Crop (Command-K). Be sure to save when you're done.
If you have a photo in iPhoto, open the photo and click the Edit button. A Crop option will appear. You can crop it to a preset size or select a custom crop size.