Hi Bill and Tweeters,
This is a classic first year female Sharpie. Nice photo.
Coopers vs. Sharpie
To me, the thing to look at first is the quality of the breast streaking. In this bird, the distinctive breast streaking is broad (wide), layered (i.e. forming chains) and extensive. Cooper's streaking is much different. In COHAs there are usually fewer streaks and they are usually longer and shaped like an extended or stretched-out teardrop. Very elegant. Most often, the background color in COHAs is pure white with the streaking dark brown creating a strong contrast. SSHAs often have a more rufous appearing breast. When you look at the two side by side, it seems COHAs are much whiter on the breast, more white than dark. In SSHAs, it is usually (not always) the opposite, i.e. more dark than light.
The "indented" forehead of the SSHA is clearly represented in this picture. COHAs don't have "foreheads". Instead they have a smooth, continuous slope from the arc of the bill up through the cere into the crown. SSHAs never do. Their profiles are very different. This bird also has a white eyestripe, common in imm. SSHAs.
The tarsus of this bird is the size of a wooden matchstick, typical of SSHAs, although some male COHAs also show this feature (never females). But the toes are extremely long, especially the middle one, perfect for catching small birds. COHAs eat more mammals and have a significantly thicker and proportionately shorter middle toe.
Adult or Immature
Pretty straightforward. Yellow eye equals immature. Brown back is immature. Rufous feather edgings are an immature feature. Streaking on breast instead of barring is an immature character. Ageing accipiters is easily done in most cases.
Male or female
The eye size dictates female. Males have much larger eyes in proportion to the head than females. They are like big saucers. I know this will catch some flack but I've handled literally hundreds of migrant SSHAs over the years and, in hand, it always checks out.
Hopes this helps,

Bud Anderson
Falcon Research Group
Box 248
Bow, WA 98232
(360) 757-1911
bud at frg.org