PHOTO-RETOUCHING SAFETY TIP

Here's a tip that many photo retouchers use do all your retouching on a layer above your image. That way, you don't damage the underlying image, and you have control over opacity and blend modes you normally wouldn't have. It's also easy to erase areas you wish you hadn't retouched. The key to making this work is to get the Clone Stamp tool (S) and in the Options Bar, turn on the Sample All Layers option. That way you can sample from the underlying image and then paint on the layer above it (believe it or not, by default Photoshop doesn't let you do that it only lets you clone from the active layer to that same layer).