Originally posted by normhead I suggest taking your bear shots when they are close to the road
I lived in Prince George, B.C. for a while, near a green belt, and in the fall the elementary schools would keep students indoors at recess because of bear sightings. Our neighbour had a sow and cub in their backyard for about 10 minutes, they got some point and shoot pictures from their kitchen window.
Twenty years ago I camped at Yellowstone with my wife and four month old daughter and I got to observe three Japanese tourists get out of their rental car and walk into the bush to look for a cub that crossed the road. They never made the news (so presumably the cub was reunited with its mother before the trekkers found it), but a park employee who went hiking on her day off was fatally mauled during that time, and another woman was seriously injured by a bison bull after she got out of her car. According to the news report her trip came to a painful end when she decided to leave the tree shielding her from the animal and make a run for her car.
Personally, if I find bear scat on the trail, I turn around. The best defence against a bear attack is a .50 calibre rifle, and it is damned near impossible to shoot your gun and camera at the same time. As far as I know, armed escorts aren't allowed in national parks either, and your chances of sneaking up on a bear are virtually zero. If they are close enough for your zoom lens, they are coming for your food and probably won't agree to pose. The grazers and smaller predators at Yellowstone are used to the smell of humans, so you can still get some great wildlife photos, but don't mess with bears.