The "Surgeon's Photo"
taken on April 19, 1934 was one of the earliest (and remains the most famous) Nessie photo hoax. But three weeks before the Surgeon's Photo was taken, the Berliner Illustrirte Zeitung
came out with a photo-feature declaring that Nessie had been captured ("Das Untier vom Loch Ness gefangen!"). It was an April Fool's Day hoax.
I recently acquired a copy of the article, so I've added it to the April Fool archive. You can see why this Nessie hoax never became as famous as the Surgeon's Photo, because I doubt it fooled anyone. Still, it's an interesting piece of Nessie history. Read the full thing here.
"The moment that the zoologists of the world have eagerly anticipated: The capture of the sea serpent of Loch Ness!"