There is a peculiarity with US copyright legislation that is called “registering your photos with the Library of Congress”.
There is no requirement to “register” your images. The copyright is yours for your pictures if you don’t as well as if you do. It is not the “ownership” of the copyright that is at issue. (or is it with “the Copyright Office” – don’t remember off hand)
Registering your images with the L of C makes an important difference for one other reason: It can have a major impact on how much money you can get if someone infringes your copyright. To put it simply, the way I understand it is this:
If you have not registered your images and someone infringes on your copyright (steals your photos, uses them without proper authorisation) then the best you can hope for in a US court is to get as much money as a reasonably license fee for the use would be.
If you have registered your pictures with the Library of Congress then you can get substantially much more money in a court case from someone who has infringed on your copyright. If you need to hire a lawyer to protect yor rights then it will of course be much easier if you have registered your images.
This came to mind when I read on APhotoEditor about proposed price changes. There is a proposal on the table that the basic fee for making an electronic filing should go up from $35 to $65. This is of course a pity but considering that you can register your images in batches with many photos it is still not very dramatic, and should not really deter someone from doing it.