There are forgeries of the colonial postal stationery, and they can be difficult to distinguish without having them in-hand because many of the things to look for are in the paper -- fluorescence due to optical brighteners, weight, stiffness, etc.
That being said, the forgeries aren't of the same print quality as the originals, and this shows up in the lack of details in the smokestacks and smoke. It's difficult to tell from the photo you posted and the
ebay photo, as neither is very detailed. With the original, there should be a thin vertical line in the rear smokestack, two in the front smokestack, and distinct lines within the base of the smoke. With the forgeries, the rear smokestack is usually solid, the front one almost so, and the smoke is just a dark blob at its base.