Generally, no, as long as you don't interfere. But local laws may vary. For example, here in Massachusetts, it's legal to take still or video images of anyone in public, but NOT legal to record audio of a person speaking without their consent. So if I shoot pics with my T1i, no problem, but if I use the movie mode I may be breaking the law, should anyone complain. I know this because of some recent news coverage of a person (a bystander) who was arrested for recording a video of police arresting someone else.