This is one of my favorite images of Rockport. The photograph is by Virginia Cleaves Little. Although the postcard is not dated, I am guessing it was shot between 1940 and 1945, based on other photographs by her.
Worth noting is that Little was the second generation in her family to produce Rockport postcards. Her father, Charles Cleaves, was a photographer who produced many postcards in the early 1900s under the imprint Rockport Photo Bureau.
According to Paul St. Germain in his wonderful book, Twin Lights of Thacher Island, Cape Ann, Cleaves established the Rockport Photo Bureau in 1906 and produced thousands of postcards. His glass plate negatives are held by the Sandy Bay Historical Society.