Does it matter what my position is, such as in the middle of a public street?
Can I use this photo in any way, as duplicating it for friends, posting it on social networks, or adding it to a blog?
Basically, What are the ethical and legal ramifications, and other pertinent information of taking pictures of humans?
What can happen if this has already occurred?
ANSWER: Depends on where you live. Privacy laws vary and so do penalties.
Where you take the photo from is irrelevant.
The real deal breaker is use. For example if you were in Haiti and the person you are talking about was a victim of the earthquake and you were to use the photo in a newspaper or for a relief organization or an show of photos you’d be pretty safe.
If the person is just someone in your town and you got an interesting photo you’d have to be careful of the use. A newspaper would probably okay–as long as the photo doesn’t demean or make fun of the person– and displaying at a photo show would be okay too.
The issue is that without a model release you are severely restricted in the photos use. You can make and sell duplicates or use it in any commercial way.
As for putting the image on the web, I’d be real careful.
The best approach is to put yourself in the position of the person you photographed. Would you be comfortable if your photo was spread around by someone you didn’t know?
As for the legal ramifications here’s the problem. Whatever the particular laws==and they general DO NOT protect the photographer–you do not want to be in the position of being sued. No matter how crazy the claim you do not need that trouble and expense of a lawyer or a settlement.
If you really like the photo and believe that its worth showing, make a print and bring it to the person. Give them the print and ask them to sign a model release. Tell them what you want to do and make your case.