One handy feature of iPhoto 6 is its ability to easily compare two photos side by side. This allows you to choose the best of two similar shots, or duplicate a photo and try out enhancements on one copy while comparing it to the original.

To use this photo comparison tool, you need to have iPhoto set to edit in the main window. Go to the iPhoto menu and choose Preferences. Set the drop down menu to edit photos in main window. Now go back to your photo library and decide on two photos to compare. Click the first one, and Command-click the second (i.e. select them both). Now double-click on one to enter the edit mode.

iPhoto will show your images side by side, ready for you to crop, enhance and retouch them. There are a few additional tricks to this as well. You can select more than two photos by just selecting more at the start (by Command-clicking). If you want to replace one of the photos you are comparing, click on it and then choose a different one from the thumbnail browser at the top of the window. If you want to add in a new photo to compare, Command-click on one of the thumbnails in the browser. To remove an image from the comparison, Command-click it in the thumbnail browser again.

A slightly different way of doing this is to edit in full screen mode rather than in the main window. You can do this by Right-clicking (Control-clicking) on you selected photos and choosing edit in full screen mode.