I think it’s fair to say that most street photographers don’t go out with the intention to portray their subjects in an embarrassing or unflattering way but it can and does happen. Sometimes it’s difficult to predict how those photographed will react, particularly when they feel the photographer is being invasive or clandestine in [his] approach. If in doubt, you can always ask the subject for permission to photograph but the inevitable loss of spontaneity may defeat the objective. The essence of street photography is usually captured in those unguarded moments of human activity – something which is inevitably compromised when a shot is ‘posed’.
In most western countries it is not illegal to take images of people without their consent, provided they are in a public place; the street, park, market etc. In these circumstances there is no ‘right of privacy’ as such. There may, of course, be a ‘moral’ consideration – for instance, should you take a photograph of someone who has just been seriously injured in the street ? While it may be valuable ‘reportage’ and a photo-journalist could see it as [his] job (or even duty) to record the event, the street-photographer, perhaps more concerned with ‘art’, may draw the line at recording someone in extremis. It is, of course, a matter for the individual photographer. There have been rare occasions, when I have decided NOT to take a photograph.
The legality and morality of when to take (or not to take) a ‘street’ photograph is an interesting question and one which usually divides opinion.