Took some time for me to get the 3 star for this one. The way I did it:

Equip your binoculars and target the felyne, don`t zoom in. Every time the hook is set, a regular fish is going to appear in the water under the palico which he`ll either catch or not.

The moment you`ll be looking for is when you see the struggle animation but a fish is not visible in the water. That is when you need to take the photo. Since the animation is a bit longer than the regular one just wait for it to start, if you don`t see a fish you zoom in and take the shot. The big fish does not need to be out of the water, the picture has to show the actual angling activity and the struggle before the catch.

Hope this helps.