Possibly the first photo ever taken: child jockey
Elecreutious Underwood Pimpleton-Wylde (1657)
Tomorrow, 9th April, is a celebration of cruelty: the 2016 Grand National.

Please think twice before betting. Think of the suffering.

Once jockeys have been pulled from the sucking glue of the birthing vats they are kept in two-foot boxes with only their heads and bottoms stuck out until the age of 12. As a punishment they often get their bottoms whipped, which become terribly scarred, as well as stained from being unable to wipe properly. Crammed side by side they cannot move, and only communicate in grunts and whistles.

From the "Rumblepoker Patented Preparation Manual" (1846) 

Technology is applied to their training. In Victorian times they were strapped to a Rumbledowser for hours each day; a Dowsee was in charge and tilted the box back and forth to get the mini-men used to the motion of being on a horse. Other cruel machines included the Rumblepoker and the Whipton-Smythe. Of course, nowadays modern technology takes over and instead a long conveyor belt is used to train many jockeys at once as it oscillates at a frequency which increases sexual excitement as the machinery vibrates, combining adaptation with positive reinforcement.

"A Gentleman's Riding Trainer" (1853)

In the past they used selective breeding to make slight alterations to each generation of jockey men. Nowadays genetic engineering is used to create jockeys the size of a toddler, but who weigh only 6 grams due to micro-pockets of air in their bones, and a reduced water content. You'd think in this day and age that kind of thing would have been stopped but the cruelty continues.
Also, horses. (Guardian; Fact Sheet)