I have an old framed bird picture, and on the back it reads "Elizabeth Taylor on the set of 'Raintree County' (M.G.M. 1957)" How can I be sure this is really her signature? How can I have it valued to sell? আরো info below...

Hi, I have an old framed bird picture, and on the back is what appears to be Elizabeth Taylor's signature. It reads "Elizabeth Taylor on the set of 'Raintree County' (M.G.M. 1957)" How can I be sure this is really her signature? Why would it be on the back of a framed picture of a bird? (is it possible this was a শ্রদ্ধার্ঘ্য used in the movie?) and what would this item be worth? I am interested in selling it. What is the best way to sell Elizabeth Taylor Memoraibilia?
Contact - emailclaire@y7mail.com
Kindest Regards,

Claire Luttrell.