This is a secretarial from a later period about 1959, the photo is actually one that Marilyn herself has said was her very favourite of all time. Cecil Beaton took it. This is still a valuable item being genuinely sent from Marilyn's own team and the photo itself being of the era and origin it is. It's possibly worth at least a couple of hundred dollars, maybe up to 500? it should be advertised as being a secretarial signed photo of Marilyn Monroe if you are selling it.
Dear Pauline and Eric, thank you very much for your assessment! I knew that it is a Cecil Beaton Photograph, but there is no stamp on it. Beatons pictures have been displayed in our art museum many years ago and I was really surprised to find the picture there hanging on the wall, my father guards like a treasure since he has been a boy. 1959 could be right. He was 14 years old when he wrote the letter. Thank you very much!!! Greetings from Germany.