Jay Tamminga wrote in to let us know that the art on the Canadian Battlestar Galactica movie poster and novel, wasn't done by Ralph McQuarrie, but is a carefully repainted image by Jack Gaughan, with brighter colors and more details added. Jack Gaughan was a well known scifi book cover painter (he did the covers and hand-lettered title pages of The Lord of the Rings books). Why it was repainted and Ralph McQuarrie's original image wasn't used, is not known.

Ralph McQuarrie's original Battlestar Galactica art

Jack Gaughan's Battlestar Galactica art (note the extra details on the viper)

      

Jack Gaughan's Battlestar Galactica art used on the movie poster and novel