Whatever it is, he's holding it towards the camera and using lens trickery to make it look as big as possible (a very common photo trick hunters use). Look at the way the snake stick tapers by about 30% as it goes towards his hand. Mentally shrink the snake as much as the stick expands visually. The snake is actually about 2/3 the apparent size - big but no whopper. Most cottonmouth adults are 3-4 feet long.

Looking at the scales on the tail ... single scales going all the way across = pit viper (in the USA). So it's a cottonmouth.

It is a cottonmouth. This photo has been widely discussed by the FB snake ID group along with the video that comes with it. This is a largish cottonmouth but is being deliberately exaggerated in the photo. Most people felt it was between 3 and 4 feet which is an average large adult.

Notice the end of the red hook. It is probably around 3 inches long. But it looks like it is as big as his head? And it looks like it is a big as the fence behind him!! Do a little reading on forced perspective to see how this trick works.