I'm not the best at identifying dogs, but think this may be a German Pinscher (?)--though the face looks a bit more of the scrappy terrier to me. Whatever the case, especially in this wide chain link collar, it looks the sort to protect one from unwanted visitors! (While also looking as if yearning to be loved.) Quite poised, but for one ear and eyebrow that twitched during the photo, resulting in a blur just there, which top me has the effect of bringing him to further life. 

6 7/16" x 4 1/4", good condition, with just some light scattered spotting to the background of the photo as visible.