Accipiter sp. Rutland 2/6/16 Photo by Ted Purcell
In this photograph, Ted's mystery accipiter does indeed appear to have a short tail in relation to overall body size. The head appears rounded at the nape and small-ish, but, again, the size of the head in relation to the body is difficult to judge while the bird is in a hunkered-down perching posture. Another possible clue to identification is the seeming appearance of dark feathers distributed from the crown and continuously downward along the nape, without a break between crown and nape (as seen in adult Cooper's Hawks). But this is not definitive, either.
According to Project Feederwatch hosted by The Cornell Lab, the eyes of Sharpies appear to be close to half way between the front and the back of the head, while Cooper's eyes appear to be closer to the front. Based on this field mark, Ted's bird is looking more like a Sharpie.
Greenfield Christmas Bird Count
Gill , MA
Okay, not such a great image, but enough to show relative head-body-tail shape.
The observer noted that the bird was the size of a Bluejay, an important clue.