I learned the art of "one man fishing" back in the good old days of CNR on the Sky.

1. Use a camera that has a lanyard. Put the camera around your neck, and tuck it into your vest or waders.
2. As soon as you get the fish hooked solidly, pull out the camera, and get ready to take a few shots of the fish while playing it.
3. Slide the fish into shallow water, or slightly onto the bank. Quickly lay your rod next to the fish, and snap away. Be carefull that the fish does not take off with yuor rod!! This lets you estimate the actual length later.

The big draw back is that by yourself you can not get pics and also measurements without harming the fish in most cases.

---
Steel-Addicted