It's (probably) legal to charge for public domain photos, but I don't believe it is to send cease-and-desist letters over the use of public works.
From the comments
>The Adventure of Tom Sawyer is public domain. Getty is publishing then the book and attacking anybody who uses the name Tom Sawyer in anything. They got caught when they filed a DMCA complaint against Mark Twain for having the book on his personal website.
From the comments >The Adventure of Tom Sawyer is public domain. Getty is publishing then the book and attacking anybody who uses the name Tom Sawyer in anything. They got caught when they filed a DMCA complaint against Mark Twain for having the book on his personal website.