Ryu, It was not the most definitive photo but it was certainly good enough. The animal could be one of several. It was largely a process of ruling out other options. I ruled out black because black snakes are black and not the greyish-green of your photo. There is no sign of a red belly. I ruled out copperhead because they have a cream belly. Brown snakes can vary a lot in colour but yours is one of those colours. Whatever colour the belly colour is the same as the rest. Also as you mention size and habitat - these are also very consistent with it being a brown snake. When confirming a sighting, I believe in going with probability. If I were a betting man, I don't think I would be risking any money by betting a large sum on saving it was a brown snake. Cheers Geoff