After reading all the replies, still feel confused. Did a google search and here's my 2 cents:
What we are discussing here is actually the 2 sides of a coin: copyright and portraiture right, and applicable to the photos that contain human faces (or even bodies only??).
Portraiture right is born with anyone, no one can take it away and no one should violate it against the law. Copyright is created when the author created the artwork, i.e. the photographer took the photo. By law, the photo's COPYRIGHT belongs to the photographer.
For the first place, no one should take the grant of taking photo of anyone without the prior permission from the person being photographed! Thus all the street snapshots, if the photographed ppl wanted to sue you, they will sure win! The trick is that most of them, maybe 99.99%, will not bother to do that, or they don't even know they are being photographed.
In the cases of wedding photography or other portraiture photography, the customers come to the photographer, asking them to take the photos, and even pay for it! This satisfies the first condition - the photographer has the permission to take the customers portraits, not violatiing their portraiture rights!
However, after the photo taking, there will be the tricky situation: the photo, film or digital, belongs to the phtographer, he/she owns the COPYRIGHT. but there is face of the customer in the photo. Because of the face captured, the customers still own the PORTRAITURE RIGHT!
In such case, the customer has no right to use the photo for COMMERCIAL USE without permission from the photographer, because photographer owns COPYRIGHT!
In such case, the photographer has no right to use the photo for COMMERCIAL USE without permission from the customer, because customer owns PORTRAITURE RIGHT!
Therefore, if no offical agreement signed, by default, the photographer owns the COPYRIGHT, the customer owns the PORTRAITURE RIGHT. If they don't agree with each other, neither of them can use the photos. Photographer publish the photos will violate the customers' PORTRAITURE RIGHT, he/she will be sued. Customers sell their nice photos to the press will violate the photographers' COPYRIGHT.
Therefore, if got faces in the photo, the photo is not belong to any one single party, it's kind of 'shared' between the two parties. To peacefully use the photos, please sign agreement in advance!
Therefore, for the couples go to studio negotiate a wedding shoot package, don't think that u r in the photos, the photos is urs. Only the faces (PORTRAITURE RIGHT) belong to you, the photo itself (COPYRIGHT) is still with the studio, u must pay to buy it if you wanted them! For the studios, if customers didn't buy the copyright, you are not free to use the photos in any way. If u want to put it as ur 'portfolio' or print a big advertisement poster out of it, please go to seek agreement from the customer first!
The best situation? Take a photo of yourself, by your own camera!