This real photo postcard is interesting not only for its view of the harbor, but also for its view of Bearskin Neck. As you can see, the ocean end of the Neck was relatively clear of buildings, compared to how it looks today.
Note the tower farthest to the right on Bearskin Neck. It appears to be the transit tower that was erected in 1892 and still stands there. However, whereas the tower today is attached to a larger building, it was freestanding then and appears to be supported on stilts. (I have enlarged the tower detail in the image to the right.)
The tower’s location was previously the site of a stone fort, erected during the war of 1812 as a protection against British warships. The fort was captured by the British in a sneak attack and dismantled, after which the townspeople fought back by hurling stones at the British. Their counterattack ended in a negotiated resolution whereby the British agreed to leave Cape Ann waters.
Even though this is a real photo postcard, it bears the imprint on the reverse of a commercial publisher, Rockport Stationery Co., which went out of business in 1913. The reverse also bears the imprint of the real photo process manufacturer, Velox, which indicates it was produced sometime after 1907. Given those two clues, I estimate this picture to be from around 1910.