Helpless monkeys are on sale for the equivalent of £3.80 in a tourist hotspot - and often go on to live in misery.
Distressing photos taken by tourist Luke Massey in Bali show the long-tailed macaques chained to cages.
The 28-year-old snapper said: "Long-tailed macaques are the most commonly found monkey for sale in Indonesia's markets.
"They are cute looking and easily attainable in the wild relatively close to cities. The demand is mixed.
"Some people buy the monkeys as babies, thinking they will stay cute forever, only to find them turn aggressive once they hit adulthood. Others buy them to train as dancing monkeys."
The animals are being sold for as little as $5 (£3.80) and largely live in misery.
"These monkeys are often tortured to learn to stand on their feet like humans, being hung just so their toes touch the ground for hours, beaten and starved so that they ride a bicycle or stilts on demand.
"Once trained they are paraded at traffic lights and busy areas, where their owners ask for money after each performance," Mr Massey added.
He added: "Youngsters are left in small cages or chained up once they reach adulthood. Some lucky monkeys are bought by well-meaning tourists to be released or given to organisations but, despite being well meaning, this usually just fuels the trade.
"Seeing a monkey in the wild is a fantastic experience. Seeing them in captivity in the markets is a horrible feeling, seeing their sadness in their eyes, while feeling completely helpless as they're chained up is awful.
"Also knowing they are group animals and they are often kept on their own."
Long-tailed macaques typically life for around 30 years in the wild.
They live in the Philippines, Malaysia, Indonesia, Burma, India and other Asian countries with warm climates.
The creatures eat insects, stems, young and mature leaves, flowers, seeds, grass, mushrooms, invertebrates, bird eggs, clay and bark.
