Some people believe a big animal lives in Loch Ness. They call it Nessie. People who report Nessie often describe a long neck, or humps that stick up out of the water. In North America, some people say a big, hairy creature called Bigfoot walks on two feet, is taller than a grown-up and is covered in long, dark hair. For both creatures, a picture is the kind of evidence that anyone can look at. Here is how some of the best known pictures held up when they were examined closely.

In 1934 a photo seemed to show a long neck rising out of Loch Ness, and it was called the Surgeon's Photograph. It had such an impact in part because it came from a respected London doctor. It was shown to be a hoax in 1994, about sixty years after it was taken, and a hoax is a trick meant to fool people. This one was built from a toy submarine with a model head and neck fitted to its conning tower, and the scene was staged on the loch. The famous "monster" in the picture was a toy. A picture that looks convincing can still be staged.

The Surgeon's Photograph was not the only picture to fall apart when it was examined. Most photos said to show Nessie turned out to be fakes, or to show other animals or objects. Many sightings at Loch Ness could be waves, boat wakes, logs, birds, seals, otters or swimming deer. In 2016 a robot drone found a 33-foot Nessie film prop on the bottom of Loch Ness, and it had been made for a 1970 movie. A prop is an object made for a film, which means that this one was built to look like the monster, not to be one.

The most famous film said to show Bigfoot was shot in 1967 near Bluff Creek, California. Roger Patterson and Bob Gimlin made a 59-second film of an ape-like figure walking. No one has verified it as showing an unknown animal, which means that no one has shown that it is a picture of one. A short film of one figure in one place leaves open the same question that every picture of these creatures leaves open: what, exactly, was the camera pointed at? A film can show a figure, but it cannot say what the figure was.

Pictures are not the only kind of report. Many reports come from people telling what they saw. Nessie witnesses number in the thousands: Nicholas Witchell counted more than 4,000 accounts. A witness is a person who says that they saw something with their own eyes. Many people who reported seeing something at Loch Ness were sober, level-headed people, such as scientists, teachers, police officers and fishermen. So it would be wrong to say that the people who report these creatures are all careless or dishonest, and the harder question is how careful people can be so sure of something that other evidence does not support.

One answer to that question is a psychological effect called expectant attention. It makes people's observations fit what they already expect, such as a water monster at Loch Ness. Scottish folklore, which is the collection of stories that a community passes along, is full of mythical water creatures, and many early Loch Ness reports seem to have been inspired by it. A person who knows those stories and sees a dark shape in the water may read the shape as a creature, and that mix-up needs no lie at all. The person does not have to be dishonest for this to happen.

Bigfoot reports can be checked in a different way, with a map. Scientists can ask where the sightings happened and then look at where animals live. Researchers plotted Bigfoot sightings in a 2009 study and found they roughly matched the habitat of the American black bear, and habitat is the kind of place where an animal lives. Some scientists think people who report Bigfoot may be seeing bears, which can stand up on two legs. The match does not prove that every sighting was a bear, but it offers a simple explanation that uses an animal we already know is living in those places.

Cameras can also show that a hidden animal lives in a place. Scientists use camera traps, which are cameras with motion sensors that take pictures by themselves, to see shy animals. By 2011 the Smithsonian had gathered more than 202,000 camera-trap photos of over 200 kinds of mammals and birds into one website. The saola, a large forest animal, was found by scientists in 1992 in Vietnam, near the Laos border. It was first known from a skull with long, straight horns that scientists found in a hunter's home. In 2013 a camera in Vietnam caught a saola, the first time one had been caught on camera there in 15 years.

As of 2019, Gary Campbell, who keeps a register of Nessie sightings, received on average about 10 reports a year of something unexplained in the loch. That is the count of reports about something unexplained. So far no body or bones of Bigfoot have ever been found, and no bones, bodies, feeding signs or droppings have been found that would support a monster in Loch Ness. Most photos said to show Nessie turned out to be fakes, or to show other animals or objects, and the most famous Bigfoot film has not been verified.

Words to know

• hoax: a trick
• witness: person who saw
• folklore: old stories
• habitat: where it lives
• verified: shown true