I was happy to add this signed photo to my collection for a very reasonable buy-it-now on eBay.
Be cautious however, there are a lot of Steinbrenner forgeries on the market. There have been certain eBay sellers with an endless supply of "perfectly and neatly" signed George Steinbrenner baseballs, many with "The Boss" inscriptions, etc.
Also, it appears that he did have a secretary sign for him at times... I often see secretarial signatures on Yankee letterhead.