Lots of people report problems with trail cams and bears. I have only had one issue with 15 cams over 4 seasons. Mostly, however, I mount my cameras fairly high pointing into a sidehill which keeps the smell above the critters and a little above easy reach despite being on level to take good pictures. (Oh, and I almost always point them north since that is most away from the sun for the biggest part of the day.) The pictures I've seen of cameras with bear problems are at bear nose height. The one I have had issues with is fairly low, couple feet up. I'm not sure what I will find when I return to that camera. I didn't realize it'd been messed with when I retrieved the last card, nor what the culprit was. The pictures show a mother bear (blonde phase black bear) with 2 cubs. 1 cub disappears, then the view is hair, ears, etc, and the camera winds up pointing into the bushes for a while. On the 2nd visit, it somewhat re-corrected the camera. My hope is, since I had another few weeks of pictures before the batteries ran out, that those bears moved on and I'll have good pictures for the rest of the season ... up 'til snow.
The most visible thing with any camera seems to be the strap attaching it to the tree. Horizontal lines are not natural. I have masked them a few ways. Little black upholstry tacks are your friend. Bland colored rubber bands, too. Can use local material like leaves and twigs covering the strap and held in place with twigs. I also bought a roll of camouflage burlap which I cut strips off of. Make the edges irregular so you're not just replacing one straight line with another. A totally separate method is to use large wood screws spaced matching the width of the bracket on the camera and hang the camera on wire thus removing the nylon strap completely. Some of that burlap around the back half of the camera, which is often solid color rather than camo like the front, can help hide the camera, too.
I have not used bear boxes / lock boxes. Its an interesting idea. One thing about it, you could paint those in whatever camo best suits your area without having to worry about getting the paint on the flash, lens, etc. Definitely worth considering.
Here is one I was sort of lazy with.
And this is what it is watching.
As soon as I'm able (July?) I'll add a plotwatcher to this area. It's incredible.
MIB