How to take a fish photo that measures well

The photo you already take of a good fish can tell you its length and weight, as long as a few things are right. None of them take extra time on the water. Most are habits that make a better picture anyway.

How fishline reads a photo

It helps to know what fishline is looking for. First it identifies the species from the body shape, mouth, fins and markings. Then it looks for something in the frame with a known size to use as a ruler: a bump board or tape, a rod handle or reel, a 5-gallon bucket, boat cleats and rails, a lure, or your hand. An adult hand is about 7.5 inches from the heel of the palm to the fingertip, and that is often enough. Then it corrects for how far the fish is from the camera, works out the total length, and runs the species length to weight formula to get the weight.

Every tip below makes one of those steps easier.

1. Get the whole fish in the frame

Nose to tail, with a little room around it. A cropped tail is the most common reason a fish measures short, because total length runs to the tip of the tail. On a long fish like a pike or a musky, step back or have your buddy step back. Do not cut it off to fill the frame.

2. Side-on and flat to the camera

Turn the fish so the camera sees its full side, not its belly or its back. Keep it level, not tilted nose up or tail down. Anything angled away from the lens looks shorter than it is, and anything angled toward it looks longer.

3. Arms in, not pushed at the lens

Everybody knows the trick: hold the fish out toward the camera and it looks huge. fishline is built to see through it. It judges how far the fish is in front of you from things like the size of your hands against your head, and scales the fish back. But the more it has to undo, the wider the range on the estimate. Hold the fish close to your chest, level with it, and you get a tighter number. It still looks like a good fish. It is one.

4. Put something of known size in the shot

Your hand on the fish is the easy one, so keep it in view rather than tucked behind the body. Better still is a bump board or a tape measure laid alongside, because fishline can read the marks directly. On the deck of a boat or next to a cooler, standard hardware does the job. On small fish like bluegill and perch, keep the reference small and close: your fingers or a ruler right next to the fish.

5. Use the main lens and shoot square

Phones with an ultra-wide lens (the 0.5x setting) stretch whatever is closest to the camera. Use the regular 1x lens, hold the phone at about the height of the fish, and point it straight at the fish rather than down or up at it. If you are shooting a fish laid on a board or the deck, stand over it and shoot straight down.

6. Light it so the outline is clear

fishline needs to see where the fish ends. Silver sides on trout, salmon and stripers throw glare in direct sun, so turn until the sun is behind you or off to one side. At night, or at first light when walleye bite, use the flash or a headlamp. A clean outline matters more than a pretty background.

7. A second angle helps

You can add up to 8 photos of the same fish to one measurement. A second shot from a slightly different angle, or one on the bump board after the hero shot, gives fishline more to work with. One good photo is enough, though, so do not hold a fish out of the water for a photo shoot.

8. Tell it what you know

When you measure, you can pick the species, say what is in the frame for scale (your hand, a bump board, a tape, the boat), and type in a length or girth if you took one. fishline treats numbers you measured as ground truth and works the weight from them. It still checks the photo and the species.

Keep it quick

None of this is worth hurting a fish you plan to release. Have the camera ready before you lift the fish, take a couple of frames, and get it back in the water. We wrote up the basics in catch, photo, release. Each species page also has photo tips for that fish, from flounder laid flat on a board to big catfish shot from above.

Ready to try it? Measure your first fish free. Free accounts get 5 measurements every month.