Unless you are directly employed to take photos or you sign away copyright in a contract, you automatically retain all reproduction rights over your own photos. This is something that prospective clients often do not realize: that they are paying you for your skill and time, but not ownership of your work. There is no transfer of ownership in that respect, and photographers are free to use the photos in any way they see fit, provided it doesn’t slander or defame the subject(s).
In the days of film, newlywed couples and other clients would typically receive proof prints to peruse after a wedding or event, usually covered with watermarks to prevent any illegal copying. Nowadays, it’s common for photographers to present a DVD full of digital images as part of their service, which can be used to create prints or share online as the client sees fit.
A DVD of photos for personal use still does not transfer copyright, so the client couldn’t, for instance, enter the photos into a competition and pass them off as his or her own. Nor would it be permissible to publish the photos, either in their original form or as part of some other creative work (a montage, for example). Whether photographers pursue infringements is always a matter for them, but it’s certainly the case that much of the world is oblivious to copyright law.
When displaying photos to potential buyers over a passworded website, you’ll want to place watermarks over your images to prevent them from being printed. Even a moderately sized web image can often produce a print of reasonable quality.
What photographers are entitled to do and what they should do are not always the same thing. If you’re in the business of photographing people, of course it is not good practice to regularly upset them. The same is true of asserting your right to publish your own work wherever you please. Let your intentions be known to the subjects of your photos as a courtesy, particularly if you’re planning high-profile publication.