Philip,
I don't know about it being a well-known image in golf history but this image is mentioned by Robert Browning in "A History of Golf" in his chapter The Argument of Pictures (p.18).
"By far the oldest pictorial representation of what might conceivably be golf is to be found neither in Holland or in Flanders but in England in Gloucester Cathedral. In one of the medallions of the great stained glass east window built for Sir Thomas Bradstone between the years 1340 and 1350, in memory of his comrades who fell in the battle of Crecy, is a figure swinging some sort of club in very convincing and workmanlike style. The window has suffered a little with the passage of the centuries; the upper part of the players head and a space immediately above it are gone and have been replaced by a blank of clear glass, but the glass is otherwise intact and the swing can be examined in detail. It is true that the club bears a much closer resemblance to a modern hockey stick than to a golf club, but the player's attitude seems to be more consistent with a deliberate and controlled swing at a stationary ball than with a blow at a moving one."
He talks briefly about a more recent stained-glass window in St. Cuthbert's Church in which a saint is represented striking a ball but wryly suggests that this provides no evidence for " believing the saint to be a golfer." to which my response is that there are no grounds for believing any golfer to be a saint …. Peter Pallotta notwithstanding!!
Interesting to see that a "man on the ground", Mark R., could not find the image whilst singing his head off! This search, then, should become a Holy Grail type of challenge in my opinion, a quest emulating knights of old, a chivalrous deed for the good of golf!
Cheers Colin