Depending on your perspective, this image could be menacing or amusing. Doesn't it look like this shark is 'smiling'?
While great white shark attacks aren't a big threat to humans in the grand scheme of things (you're more likely to die from a lightning strike, alligator attack or on a bicycle than from a great white shark attack), white sharks are one of the types of sharks that are most likely to "attack" humans.
This is more likely because of their investigation of potential prey than a desire to eat humans. Sharks prefer fatty prey with lots of blubber like seals, and whales - and don't generally like us - we have too much muscle!
The great white's predatory behavior is poorly understood, but scientists are beginning to learn more about their curious nature. When a shark is presented with an unfamiliar object, it will "attack" it to determine if it is a potential food source, often using the technique of a surprise attack from below. If the object is determined unpalatable (which is usually the case when a great white bites a human), the shark releases the prey and determines not to eat it. This is evidenced by seabirds and sea otters with wounds from white shark encounters.
All talk of attacks aside, in reality, sharks have more to fear from humans than we do of them. It is estimated that up to 73 million sharks are killed each year for their fins alone. In contrast, about 4 humans each year die from shark attacks.