A couple of years ago, I attended a photography workshop in Chicago. The instructor was really big on photographing strangers. He felt it was important for photographers, who tend to be introverts, to overcome their shyness and photograph strangers. Inspired, I set off for the local farmers' market the following weekend to photograph people. The first vendor I asked was very nice and cooperated willingly. The second one was a very interesting looking character who may have had a police record. In any case, he flatly refused to let me take his photo. This took considerable wind out of my sails, and I packed up my camera and went home.
As I look through my Flickr photostream of some 2600 pictures, I can find six photos where I had some level of consent from a stranger before clicking the shutter. It may have just been holding up the camera and getting a nod, or actually asking to take a picture. Two of these photos were of the same guy feeding pigeons in Daley Plaza in Chicago. I have taken a few other street photos without the subjects' knowledge. I hope in the future to include more people in my photography, as I think it adds an element of interest beyond that provided by inanimate objects or flora and fauna.