It's interesting and I totally agree when you say "I think thinking bad thoughts about ourselves becomes a habit. If that's true, then thinking positive thoughts can become a habit, too."
This doesn't really have to do with body image, but it goes along with how thinking can become a habit, in a positive or negative way. I had the hardest time quitting smoking.. I'd last what, maybe a week and be back at it again. Well the last time I truly attempted to quit had, I got to a year smoke free (and then I started again BAD ME! I know I know.. ) but the way that I made it a whole year, was because I wrote little notes around my house that I go to often. Bathroom mirror, fridge, front door, alarm clock etc. And the notes said things such as "I don't want to smoke" "I want to be healthier" "I don't need cigarettes" "I feel more energized without smoking" etc etc... and every time I came across a note through out the day I would have to read it out loud 3 times. And I gotta tell you, after a few days to a week of this, it really made a difference. It got me from 3 days of not smoking to a whole year! I changed the way I was thinking. So we can all do this with our body image, self esteem, confidence, anything really. Choose to change your negative thoughts to positive ones. (even if you don't believe them right away, after telling yourself over and over and over and over again, YOU WILL BELIEVE IT.) Those first days of telling myself that "I don't want to smoke" - ya right! I didn't believe it, but I kept telling myself, and 3 weeks later when I was around people smoking, I was offered a smoke, and I turned to them and said "no thanks, I don't want to smoke"

and by that point I meant it. And whenever it began to get difficult again I brought out my little sticky notes and put them up on my fridge and mirrors for a couple days.
I know it sounds kinda silly, but it really is a matter of changing your thought process. We all have trained our thoughts to think negative things, so why can't we re-train them with positive ones?!