I was having trouble with a portrait today, specifically with a persons left eye which was half closed in an otherwise great portrait. So I did a quick Google and came across this simple fix using Photoshop by lyn mckellen for Lynda.com
If you use Photoshop, I imagine you probably know all about the amazing healing brush, which lets you clone one area of an image (called the source) onto another area and seamlessly merge the results. (Or, at least, that's the idea. Some results are more seamless than others.) But do you know about the healing brush's partner in crime, the Clone Source panel? It lets you set the position of the source as well as scale it. Better yet, you can flip and rotate the source.
Source (http://www.deke.com/) (image Simon P M Johnson)