[Butch Cassidy Slept Here]

I did think about taking a photo but did not want to embarrass the man.

There's no need to take a pic showing the face of the obese passenger. The Small Claims Court would only be interested in to what degree did he intrude upon your seat. So, accordingly, the pic should, in effect, be a close-up of the seat cushion area.

Beware of the possibility the flight attendants might try to make an issue of your photographing the seat cushion. Some months ago there was a woman who used a cell phone to video a fight (or shouting match) on a Jet Blue flight to Las Vegas. The flight attendant asked the woman to delete the video. When she refused he had her arrested. Since the video has found its way onto You Tube I shall assume the Las Vegas/McCarran Airport Police did not try to confiscate the video. The moral: If you take a pic in-flight, and you're lucky enough to be on a flight with wi fi, get that pic onto some server as fast as you can. Otherwise, try to hide the "card," or give it to a friend.