Designed, painted and signed by Dorothy Knapp. I have never seen another. All the covers after 1953 and before 1980 were painted in the 1980s including this one. Her son, Wally, went to shows and bought uncached covers for his mom to paint. She did not do all of the issues between these dates.
Some are unique, some she did a few of. In any case they are as rare as the covers she made in the 1940s for the 1920s and 1930s issues. See scans - inspect please. This item is in the category "Stamps\United States\Covers\FDCs (1951-Now)\1961-70".
The seller is "weiszcovers" and is located in this country: US. This item can be shipped worldwide.