Boxing Memorabilia question

[ForeverZero]

I have a fight poster of Ali vs Foreman , and to make a long story short .. I was told it is worth 5000 dollars I was kinda shocked cuz I was thinking 200 would be a lot so anyone know how much this is worth it is 48x40 .. I seen a 18x15 (something like that ) and it was worth 1500 so this got me thinking . I have had it for 20 years and was framed . It does have creases from being folder for some time ... Also is there a way to find if it is a fake ...

http://i125.photobucket.com/albums/p67/saibot77/ali-foreman.jpg