When filming in a city can you get in trouble for getin shoots of strangers walkin by?

The general rule is that as long as the people aren't recognizable and their privacy hasn't been compromised then you're okay. That's how you can show an actor walking through Times Square along with a thousand other people without having every single one of them sign a release allowing you to photograph them. However, since that doesn't keep a person whose face is clearly visible from suing you for damages, a smart producer will do one of two things. If possible, anyone in a scene - even extras - will have signed something saying you have permission to show them. If it's not possible, then you'll put up clearly visible signs that say "Filming in progress. Entry to this area gives your implicit consent to have yourself photographed and shown in a motion picture."