You will need to speak with MGM to get permission, because MGM owns the copyright in Some Like It Hot. I have attached a link below.
You will also need to get permission from the Estate of Marilyn Monroe for Marilyn's likeness rights.
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The litigation surrounding this celebrity is active and in flux. Just take a look at this suit that is still going on. http://www.law360.com/articles/409970/marilyn-monroe-estate-licensing-co-end-fight-over-photos
Is this a frame of film from the movie or a picture taken by a photographer on set? If it is a movie still, it might be owned by the movie producer. If it is an on set photograph, these guys might own it.
Consult with an attorney before entering into any sort of licensing agreement.