One would think that if the person is in plain view, and if the location is such that there is no expectation to privacy, then it wouldn't be illegal...but since I don't know the answer, I guess I'm asking on a legal forum!
Criminal Defense Attorney
It is not illegal to take photographs of people as long as your are not taking photos down their shirts or up their skirts. Also, you cannot harass people by getting in their face or continuing if they ask you to stop. Using their image for your financial gain may be another problem. There may also be the issue of the police / woman thinking that you are doing something wrong (or feeling that you are harassing them.) You must be asking this question for a reason. If you are taking the photos to fulfill some sexual desires, you could run into trouble.
Many states have, as an incident to normal rights of privacy, a civil action for taking a person's likeness if you are using it for a commercial purpose. Also, there may be other legal problems depending on the amount of intrusiveness, or the method you take your pictures. You should consult an attorney in your jurisdiction, who may give a free consultation. Also, "stalking" is often incorporated in to the criminal (penal code) and may be brought up again based upon your methods and the intrusiveness (for example, following or harassing a person while taking their picture. You can search these topics by putting the name of your state and key words like stalking, appropriation of likeness, invasion of privacy. Good luck..