I always ask permission. Even if they’ve already walked past me. I most often show them their picture. People tend not to reject it because I’m not some creepy guy with a camera hiding to get a photo. I’m in the middle of the street, in their face. By the time I post anything to my blog, I’ve almost always gotten approval from my subject. I keep a stack of business cards and encourage people to email me so that I can send them their pic. Rarely this doesn’t work. Most people are happy because I’m happy. They aren’t afraid because I’m not afraid.