In this old view of the harbor, note the fishing schooners docked alongside a large building on T-Wharf. The building was the freezer and cold storage building of the Interstate Fish Corporation. The building was constructed in 1918 and destroyed by fire in 1923. As the news clipping to the right reports, at the time of the fire, the building had been unused for two years.
This postcard bears a postmark of 1930. Given that the building it shows stood only from 1918 to 1923, and was out of use after 1921, it seems a safe guess to put the date of this picture as 1920.
The postcard is addressed to a Mrs. Pool in Vermont. I note that only because Pool is family name that stretches back to Rockport’s earliest settlers. Reportedly, the town’s second permanent settler, in 1700, was John Pool. He build the town’s first framed house and its first saw mill, and was the first to build a vessel in Sandy Bay. So, perhaps the person to whom this card was sent was married to a descendant of his.
The postcard was published by Rockport Photo Bureau and printed by The Albertype Co., Brooklyn, N.Y.
Vintage Rockport 
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Built in 1918, by 1921 it was unused and empty, and it burns in 1923. Insured for $235,000 which is $3,250,000 in 2014 dollars. George W Perkins retired from New York Life Insurance in 1905 and also worked at JP Morgan. (He knew his way around insurance and a dollar.)
The fire started unknown origin on a windless night. In minutes the entire building was consumed.
Looks like George fixed a mistake he made. I wonder why he was not called an insurance magnate and not a fish magnate since it did not seem he was all that successful at the latter but very good at the former.