These prints have been available on ebay and other online shops ever since they were signed. They are authentic.
The only thing I would consider is the faint Doohan autograph since he is the "key" one for that poster. Depending on the price I would not want to pay top dollar for it. It is not like he is super rare and the others are still signing. So I think bottom line is if you are comfortable with the looks and the price.