You might be able to make the case for copyright violation when the word cash was used. I would think you making something for your own exclusive use like a desktop is no problem. Perhaps it is still violating the letter of the law but no one would mind?
Then you should think again, or consult a legal professional in your jurisdiction, because my reading of the US copyright law has me believing that offering a third party's image for monetary gain without the copyright holder's permission is illegal. My reading also has me believe that if it's an image from a book that's registered with the US Copyright office putative damages apply which puts the potential liability in the five to six figure range.
I do a fair amount of computer forensics, often dealing with intellectual property issues.
You'll find that most photography forums that include people selling images for money will have people who're more familiar with the copyright issues than the average person, and who understand what it means to have their images abused by folks who don't have permission.