looks like a brown snake but if your dogs leg is swollew no matter if it is a bite or not and you seen concerned maybe you need to take it to a vet on the other hand if you can touch the swelling and see if it is infected then you don't need to go to the vet you can take care of it yourself, if you don't know how I am sure people here can help you if you need help now I can tell you what to do. But you need to look at it first and go from there. show us what the swelling looks like.
Rhayden
PS if it is poisonous and your dog is bit it will show signs of the poison very fast if it has been days and nothing then is is safe to say it was not poisonous and the wound need to be taking care of