It is unfortunate (and somewhat perplexing) that the seller will not divulge the name of the other subject in the photo. If that person were named, and could be confirmed with a cross reference photo, and that person could also be linked to Ty Cobb, then the seller would be wise to give up that info.
One quick question to those who collect vintage photos... if this were actually confirmed to be Ty Cobb, would it be worth the asking price of $900?
(and since this might be one of those threads were a name should be included, my last name is W_olff, minus the _ 
)