As a general rule (and putting aside everything from the Official Secrets Act to the Sexual Offences Act), I can take a photograph of whoever I like, whenever I like, as long as I'm in a public place (or anywhere else where there are no restrictions on photography). For example, if you leave your curtains open, I'm perfectly entitled to take a photograph of you, through your window, as long as I'm on a public footpath.
Once I've taken that photograph, I'm generally free to do exactly as I like with it, including posting it on a website. There are certain restrictions which, for example, mean that I can't take a photograph of a celebrity and use it, without permission, in an advertising campaign. I must also ensure that I don't use that photograph in a defamatory manner (e.g. if I manipulated the photograph to show that you were engaging in some strange sort of sexual activity, the laws of defamation would provide you with a means of redress through the civil courts).
In general, though, anyone can publish your photograph on their website without your permission.
Chris