''In terms of contemporary fine arts imagery, horses don't have a great track record,'' said James Danziger, the founder of Artland.com, which plans to sell museum-quality prints by artists on the Web beginning next month.
''Steichen photographed some models around a horse,'' Mr. Danziger said. ''And Annie Leibovitz has made good use of horses in her portraits. But I wouldn't say that the horse is the most potent symbol in photography. Nevertheless, as a prop in fashion, it seems to be this year's model.''
And he offered a little timeline: ''Until last year, the baby was ubiquitous. Then we went into a dog phase. Now it's the horse.''
Mr. Danziger anticipates that Artland's limited edition of a Walter Chin photograph showing the model Gisele naked on a white horse will sell briskly, at $195 or $295, depending on size.
I asked a spokeswoman for Calvin Klein about the meaning behind the October mailing. Was there an implicit connection between a horse and the look of Calvin Klein clothes? Did he consider himself a dark horse? And so forth. She replied, ''The horse isn't really relevant to us.''
She suggested I call Steven Klein, who took the pictures and was the art director for the cards, which were actually miniature versions of a Calvin Klein ad campaign that ran in the fashion magazines last month. The pictures are beautiful and distinctly unschlocky, probably because Mr. Klein (no relation to the designer) showed his horse without a beach or a girl.
''Look, I have horses, I love horses, and I've been photographing them in my own work for a while,'' he explained. ''It's natural to photograph things you're involved with.''
The star of his campaign for Calvin Klein is El Star, 11, a Trakehner that belongs to Steven Klein's pal Kelly Klein, who is herself well known as the horsy muse to Calvin Klein, her estranged husband.
''El Star is jet black with a white star on his face and three white socks,'' Ms. Klein said. ''He's incredibly talented, and he's my favorite show horse right now,'' she added, explaining that she was champion on him in her division at a recent show. Ms. Klein said that El Star shone as a photographic model: ''Steven shot him on white seamless, and El Star was very good. He's very aware of his surroundings, very sensitive, and he just stood there, kind of studying Steven.''
But why horses, why now? Ms. Klein explained that, of course, she was predisposed to love all horse references, as at the Stella McCartney show last month. ''She really had me in those first minutes,'' Ms. Klein said. Probably the horse's deployment in fashion means what it always has, a handy stand-in for preadolescent female sexuality. Or, as Ms. Klein said, ''There's just something about a girl and her horse.''
Ms. Roi doesn't ride, and neither does Mr. Adrover, who said he used horses as shorthand for a certain kind of Americana. ''My show had four parts, these different views of America,'' the Spanish-born Mr. Adrover said. Two of them were horsy: one Western and one on street style. ''With the street, you see the polo on the homeboys, and you just want to make it bigger, you know?'' Mr. Adrover said. ''The West was the Western shirt, and I've never seen the West, but I have this image, you know, this projection, like the Marlboro campaign.''
A spokeswoman for Stella McCartney said that Ms. McCartney loves to ride, that her mother loved to ride and that Ms. McCartney had become interested in the work of Gericault and the English painter George Stubbs, both of whom had a penchant for painting horses with manes down to their ankles. I mean hocks.
''Everyone in fashion is striving for this kind of perfect beauty, and horses have it without any effort,'' Steven Klein said.