Copyright permission letter
 

I have a commission of a posthumous Government official from a small town in Georgia. The photo that I have to use is a proffessional photography studio's photograph. I need to compose a letter-of-permission allowing me to use the image. This letter is to be signed by the photographer and/or studio manager and will need to state that they are allowing me to paint a portrait from their copyrighted photograph. Does anyone have advice on what it should say or where I might find a template with the appropriate wording so as to protect myself legally?