Shatner is an avid rider and master horseman, a fact he showed off to great effect in STAR TREK: GENERATIONS. He keeps a stable in Burbank, not far from WB studios. Yes, his direction of STAR TREK V: THE FINAL FRONTIER left much to be desired. But some of the blame also lies at the feet of Paramount, due to the success of Nimoy's TREK IV. The humor inherent in that film's success led to the awkwardly misplaced comedy in Trek V, although I personally feel that the story itself was flawed from inception.
I have a vast library of Trek reference that I collected through the years independent of my doing any Trek illustrations. But this library came in handy when I was hired to draw the Trek covers. Why WOULDN'T I use it? Occasionally, I did augment the photo reference with my own knowledge of anatomy, as well as my memory of the specific characters and actors I was rendering (how they moved, and other identifiable characteristics), just as I've done on Harry Potter, Wizard of Oz, and other likeness-oriented properties. The make-or-break in the likeness "game" is when the artist has to depart from photography and his/her reliance on reference becomes evident. Too many times a specific shot just isn't available, and you have to use your imagination to fill in gaps.