In the hot jungles of Thailand, forest rangers   came across a terrible sight one day in 2010. Two tiger cubs   lay dead in a wildlife preserve  . The rangers were too late to find the cubs' mother. All that remained of her was blood on the ground. Poachers  had poisoned the tigers. Then they ran off with the mother's body. If the rangers had not arrived, the poachers would have taken the cubs too.         Tigers in trouble  One hundred years ago, there were about 100,000 tigers. Today, only about 3,200 remain in the wild. Poachers are a major problem. These killers sell tiger fur, teeth, claws, and other body parts in illegal markets. One tiger's parts can see for $50,000.         Because they hunt in huge jungles thick with trees, poachers are hard to find. But they must be caught, says Elizabeth Bennett of the Wildlife Conservation Society. This group works to help endangered animals.        Tiger "fingerprints"        Finally, after many months, the rangers spotted  the poachers again. After an exchange of gunfire, they arrested the criminals. Soon, the police found evidence that the poachers had killed again. The evidence came from a cell phone. On a poacher's phone, police found photos of the men posing   with a dead male tiger. The poachers claimed that the photos were from a nearby country where tigers aren't protected. But another photo told a different story. Deep in the Thai forest, the rangers had set up camera traps, which take photos when they sense movement. A camera trap photo showed the same male tiger walking through a wildlife preserve before he was killed. That meant that the tiger came from a protected area. But how could police prove it was the same tiger? Tiger stripes are like fingerprints. No two patterns are the same. When police compared the photos, the stripes on the tiger's head matched. The poachers were given up to five years in prison. That might not seem like much for killing tigers. But since the poachers were caught in July 2011, no tigers have been killed in that wildlife preserve. What do we know about the camera traps set up in the Thai forest?
They are useless. They play an important role. There are tigers' fingerprints on them. The poachers know how to avoid them.