I don't think he's as big as 300 lbs.. Look at how big his ears are compared to his head, if he were 300 lbs his head would look shrunken. It is a difficult picture to judge, but basing it off the ears I'd say 250ish.
Like it's been said, the picture is deceptive.. I shot a 325 lb bear, he was 6'3'' from nose to tail. He looked bigger than this bear so it really is hard to judge. A side view would be better because then we could see his length compared to his girth.