In 1960, Tim Dinsdale recorded a 16mm film of a Nessie that, to my mind, remains the most solid evidence that there are large, unidentified creatures in Loch Ness. The film has been discussed in many places, primarily of course in Tim's book, "Loch Ness Monster".  My comments on it are in the article
"The Case for the Loch Ness Monster: The Scientific Evidence"

The film shows a large hump moving away from the camera, turning to the right, submerging, but continuing to throw up a sizeable wake. A break in the film at this point is owing to Tim's having to rewind the camera's clockwork motor. Then the wake is seen again, moving now from right to left, with nothing obviously visible above the surface.

The only non-Nessie explanation the disbelievers have been able to put forward is that
Tim filmed a boat which, under the lighting conditions then prevailing, somehow didn't
 show up on the film while the wake did. However, various computer enhancements of
 the film have failed to reveal anything like the shape of a boat.

Tim had given me a 16mm copy of his film, and I recently had it scanned onto DVD. Frame-by-frame viewing of the right-to-left wake confirms that there seem to be fairly regularly spaced splashes, every few seconds, that seem to be TO THE SIDE OF THE WAKE, consistent with Tim's interpretation of them as "paddle strokes". However, the resolution
of this commercial scan is not sufficient that I could be completely certain about this.

However, it IS certain that there is no boat making this right-to-left wake. A faculty member
in the Computer Science Department at Virginia Tech was good enough to scan a number
of frames at higher resolution and to examine them under various types of enhancing techniques to look for shapes and to vary the contrast. There is no boat making that wake.
A sequence of 8 frames is shown below, which illustrate that fact.
(Ignore the apparent horizontal shifts of the wake from frame to frame, the frames are not aligned precisely, because for enhancing, everything except the immediate region of the wake was cut out; no attempt was made to align the wake exactly within each frame.)
The Dinsdale film can now be watched over the Internet at

That link is also on the website describing the biography of
Tim Dinsdale by his youngest son Angus:
The Man Who Filmed Nessie --- Tim Dinsdale and the Enigma of Loch Ness
Adrian Shine has claimed that the hump filmed by Dinsdale was actually a boat.
I explained in an Internet discussion why Shine is not to be believed.