Katrin Eismann is a world class expert on photo retouching. She is one of the best of the best. In 2005 she was inducted into the Photoshop Hall of Fame. Anything she writes should be high on your reading list if you are serious about making the most of your Photoshop skills.
Adobe Photoshop Restoration & Retouching (3rd Edition) has become a classic and it is is now in its third edition. You would be hard put to find a better book on Restoring and Retouching photos with Photoshop. Once you’ve learned the basics of Photoshop, this book is a must read. Just look at all the 5 star ratings at amazon.com and read the glowing reviews.
Eismann is an “internationally respected teacher and lecturer on photographic imaging, restoration, retouching, and the impact of emerging technologies on photography and the arts. Katrin received an undergraduate degree in photographic illustration from the Rochester Institute of Technology and her Master of Fine Arts degree in design at the School of Visual Arts in New York City. Her other books include Photoshop Masking & Compositing and Real World Digital Photography (2nd Edition).” (From the book’s back cover).