International laws are all different, but American laws are generally among the most permissive. For example, newspapers don't have to get consent forms for everyone who happens to appear in a photo of a public venue. I don't think Google was legally obligated to blur faces in its Street View coverage of America, but it was likely the extremely wise thing to do (nothing stopping government from passing new laws) [0]. But documentaries
do -- I'm honestly not sure if that is legally the case or if it's done out of precaution, obviously the majority of TV news and newspaper photos don't blur random people's faces. And for things like the "Ali G Show" [1], you can bet all of those people who were unblurred had signed a release before entering that bar.
In contrast, I know that in the EU, architects have copyright on their work, which means you can't photograph the Eiffel Tower at night and share the photo, legally, without consent [2]
As to how you know if your photo is being used commercially...obviously there isn't a push-notification service (yet) that sends an alert to your inbox. You would just have to notice the commercial usage, as what happened when the teenager who was captured in a CC-licensed photo on Flickr found herself in a Virgin Mobile campaign
[0] https://www.cnet.com/news/google-begins-blurring-faces-in-st... (warning, autoplay video)
[1] https://www.youtube.com/watch?v=Vb3IMTJjzfo
http://www.thefrisky.com/2009-07-15/how-sacha-baron-cohen-ke...
[2] http://www.politico.eu/article/banned-taking-pictures-of-the...