Fake.
I myself am quite convinced that there are a group of plesiosaurs in the loch. I am not sure how they got there (well.... QUITE sure, anyway), but I know they are. That said, however, the alleged nessie head and neck shot at hand is quite fake. As has already been mentioned on this board by someone, the suspicious lack of ripples is most certainly another nail in this photo's coffin. Moreover, the image seems to be composed of both a drawing or a multi-copied photograph of what appears to be a saurapod, not a plesiosaur; I am sure that somewhere out there, there is an illstrated dinosaur book of some sort containing that image.
However, the background, as well as most of the lake itself, are real.
Anyway, plesiosaurs do not have thick necks as purported in this hoax. They have necks that are a bit more slender. The same is true of the head.
And what would a plesiosaur (more precisely, an elasmosaurus) be doing with its head and neck out of the water, with its mouth gaping wide? Sun basking?
Honestly, even when I was a little child I perceived this hoax to be more of a drawing or a painting than a photograph.