It was the artwork for the mock up of the 2nd edition WC:CCG box... which was never actually made. This piece of artwork is originally from the Heart of the Tiger promo, available at the 1995 GenCon.
It's not the same as the WC3 ChromArt, either (the aforementioned posters) -- that was the Excalibur escaping from Kilrah and the WC3 box proper.