Regarding the validity of copyright protection, under the 1978 revision of the U.S. copyright law, copyright is give to every creative work as soon as it is put in fixed format (e.g. picture saved onto a disk). It is not necessary to record that copyright with the U.S. Copyright office in order for it to be protected, nor is it necessary to place a copyright notice on the work. Under the OLD law, if something did not have a specific copyright notice, it was assumed to be in the public domain, but they changed that so that a work has to either have a copyright prior to 1923 or has to carry a specific notice placing it in the public domain for it to be so.
However, if you don't pay the fee and register your copyright with the copyright office (this is in the U.S. only, I have no idea how other countries' copyright laws work) the damages you can sue to recoup are limited to actual, provable losses. Registering it opens you up to being able to sue for a lot more money.
But it is expensive these days, so waiting until you have a large number of pictures to register as a collection might be a good economic compromise.