The best way is to keep the fish in the water. Kneel in behind the fish and if necessary hold the fish by the wrist of the tail. Usually a fish will be tired enough and be calm while the photo is taken. Dont take more than one or two pics. Keep the fish in the water. After the photo the fish can be held*in the water* facing upstream. The fish will right itself and you'll feel it regaining its strength . When it does slowly release your grip on its tail. Most of the time they will swim slowly away to find a safe place to rest.

If a fish is taken out of the water they generally panics, even after you put them back in the water they put much more effort into getting away and often get away before being fully revived. They probably survive anyway but why take the chance. A fish being alive is more important than a perfect glory shot.