A picture of you (rather than one made by you) involves 'personal rights' or 'rights of publicity', rather than copyright. Out in public, you basically don't have any (in the US), the open air is considered fair game for anyone to record images. BUT that does not mean your image could be used to sell a product. Commercial photographers will generally ask for your signature on a release document, perhaps in exchange for a fee. Art/documentary/news photography is more of a free-for-all.