I'm certainly happy to eat humble pie on this, and will stand corrected if wrong ofcourse but that croc just doesn't look like a real big (17+ft) croc to me.
Generally most big 15+ footers I see have some body parts missing; hind foot/feet, parts of the tail, big scars from fighting etc. I've tried to enlarge the pic supplied but am unable to.
Also, the really big crocs, 17+ft, have lost most of the vibrant colouring shown in this animal, being mostly darkish brown to almost black in some cases. I know that the water they live in will dictate this to an extent but the croc in this picture is far too colorful for an aged animal to be 17+ feet.
(them African lizards MAY be a little different to our Aussie "snappers").
Also, from as best I can see in the pic provided the teeth don't display the shortness and girth displayed in very old crocs that have been around long enough to reach 17+ft. In the pic they look long, sharp and pointed indicative of an animal in its prime.
The girth of the stomach and rear hind legs is missleading and tends to indicate massive overall size, but having personally handled these animals I can tell you that even a relatively small croc (13ft) will dislpay mass in the gut girth and rear leg girth when displayed in the manner in which it has been in this pic.
If I were forced to make a call from nothing more than the information provided, the one pic, I ,as Ole Bally has allready suggested, would have said 14, maybe 15ft.
Hope I'm wrong and somebody took one of those truely legendary monsters of the deep.