INAL, not legal advice:
The definition of digital forgery references the existing legal code's definition of "Intimate visual depiction", which is defined here: http://uscode.house.gov/view.xhtml?req=(title:15%20section:6...
So if you take an otherwise legal picture of someone, and add a filter which, eg, gives them a big forehead, you're fine. However, if you take a picture of and use it to create realistic porn of that person, that can sue.