If you've ever needed to combine a few group shots to get an image where everybody is smiling and everybody's eyes are open, you'll appreciate Auto-Align Layers. Sure, you can manually align layers, but when you run this command, Photoshop does all the hard work for you by examining the selected layers and aligning them so identical areas overlap (see Figure 7-21).
The Auto-Align feature isn't magic; the angle and the distance from the subject in both shots need to be the same for it to work. However, in Photoshop CS5, this command takes a look at the lens correction profiles specified in the new and improved Lens Correction filter (Video), which helps this tool do a better job of aligning layers.
Once you've gotten your images into the same document (on different layers), select at least two layers by Shift- or ⌘-clicking them (Ctrl-clicking on a PC), and then choose Edit→Auto-Align Layers (this menu item is grayed out unless you have at least two layers selected). In the resulting dialog box (Figure 7-21, top), you can choose from these alignment methods:
Auto. If you're not sure which method will work best to align your images, let Photoshop decide. When you choose this option, Photoshop picks either Perspective or Cylindrical, depending on which one it thinks will create the best composition. It usually does a good job aligning your images, though you may notice some distortion (as explained in the next two bullet points).
Figure 7-21. Top: ...