Captain Spandex on 28/9/2015 at 04:47
As long as the image is reasonably large to begin with (the one you posted actually fits the bill), if you have a program like Photoshop, you should be able to stretch it to poster size without losing too much quality and without any pixelation. That's what I did, and my poster turned out great. I had it done at Costco for all of $10.
(Now, if only someone would do a decent scan of the art for Thief II)