Orlando on his 333 images tumblr site has recently done a whole sequence of posts on the wooden horse torture and its numerous variations. Historically this was a punishment used on men, but he was frustrated to find very little male submissive imagery that he could post. Instead, in modern BDSM porn, it’s almost always female submissives who are portrayed taking the ride.
I think it’s possible to say the same thing about almost any form of BDSM play – there’s always a lot more female submissive imagery than male. But he’s right, the horse does seem particularly sparse in this respect. However, two artists did spring immediately to my mind who I was sure would have something suitable: Augustine and EmmaS. Both specialize in depicting all sorts of tortuous apparatus for the male body. Sure enough, a trawl through my collection popped up a couple of relevant images.
The Augustine one is below. As you’d expect from him, a simple horse torture isn’t good enough, so there’s all sorts of extra tubes and gags and pumps involved. But the metal horse is clearly a key component. The EmmaS one is more disturbingly graphic and brutal, as is typical with her work, but if that doesn’t bother you then it’s available here.