This photographic cancel of the USS Tennessee was mailed to Mr. M.M.Grey on Aug 18 1931.
It has additional cancels on the back of Charlotte, NC Aug 26 1931 and Parcel Post.
There are small black bits showing along the edge of the curved back of the envelope. They look like photograph developed. This makes me think that Beazell had a jig for developing the photos, with a negative of an envelope shape. This would have given a guide for cutting the envelope shape out of the photographic paper.
The Crosby-Beazell cachet covers were unique because of the high quality of the ship photo on the cover. This was achieved by using photographic paper to make the envelope. Beazell was a photographer and Crosby collaborated with him to develop the ship photos onto the paper, which afterwards they converted into an envelope. Then Crosby arranged for the envelope to be cancelled aboard the corresponding ship.