What Breed is My Dog?

How can I tell what breed my dog is? She was a stray before I adopted her off the street. She is all black with a small white patch on her chest in the shape of an angel. She has a short tail (I ain't sure what happened to it or if she was born that way). She has large ears, one blue eye and one brown eye, and medium length snout and large paws. She is, from what the vet says, about 2 months old.

By Robert