While considered less dangerous than their grizzly bear counterparts, black bears are not to be underestimated. They have an uncanny sense of smell and good eyesight, and are extremely powerful. It is easy for some people to confuse a large brown or cinnamon phase black bear with a grizzly. The most notable differences are that black bears have smaller heads in proportion to their bodies, and do not have the distinctive grizzly hump at the shoulders. Black bear claws are also more curved, making them extremely efficient tree climbers.
Sources: The American Bear Association, americanbear.org; The Bear Planet, bearplanet.org.
Photo credit: Don Jones (except in slide 4)