This is just a thought that struck me because when I shoot weddings, I have a clause in my wedding photography contract that basically says that I own the work and the client buys the prints only. So I feel comfortable with putting a © on the wedding pics. but for just stuff I take during my leisure, I'm not so sure.
Canada and Austraila have an odd twist in their laws, in that the client who commissions the photography owns the copyright unless the contract explicitly transfers it to the photographer.
For all other countries that are signatories of the Berne Convention, photographers own the legal copyright the instant it is created unless it is explicitly transferred to another party.
In most of the Berne Convention signatory nations, the phootgrapher owns a "moral" copyright that cannot be transferred. This means that even if the photographer transfers the legal copyright to another person, the photographer (not the copyright holder) can always claim authorship; whenever the copyright holder publishes the image, credit (if given) must be given to the actual author. In the US (and maybe a few other nations), however, the owner of the copyright can claim authorship.
Although the creator may hold legal copyright from the moment of creation--and this does not hinge on how or even whether he marks it--different nations have different laws as to how copyright is made known to the government so that it can be legally enforced. In Finland, for instance, it's necessary for the creator to publish the work in some way in his own name; when the work in his name has been made public, that's considered adequately "registered."