The Gimp is a free image manipulation program.  It has a featureset well beyond what most of us need, with tons of available help, tutorials, plugins, and documentation available online.  There are even a couple of books published about it.  Unless you're actually being paid to enhance pictures of real women into supermodels, I'd bet that GIMP is more than capable of doing the job, and of course it's much less expensive than Photoshop.

I promised a couple of books about Gimp.  There's this one (Grokking the Gimp):

And this one (Beginning Gimp):

You can download Gimp at this url.

You can download PORTABLE Gimp at this url.  Portable apps dont have to be installed to run.  ;)

I've collected some GIMP links on Blinklist for your pleasure.