In kayak tournaments, we use the CPR (catch, photo, release) format all of the time.
Most tournaments specify a standard board like the Hog Trough. We turn in inches instead of pounds.
For the token, just write a code on your hand with a sharpie...the code is given at launch time. When you hold the fish on the measuring board, the code is right there in the picture.
Craig
Proven measure for kayak tournaments, and new to the boating world. Take the 5 longest from pics with the token. Eliminates the potential problems with scales being off. I would add one thing. The token would identify the tournament day and there needs to be an individual identifier as well if everyone is competing individually and there could be more than one in the boat. I would standardize on the measuring board like a Hog Trough. Not all boat boards have inch fractions, and it could come down to fractions to determine the winner.