It's a little more than that, actually.
As soon as you set something down in "tangible" form, it is *automatically* copyrighted. You put the notice there to tell people who it is that has the copyright (and what the date on it is), not to "make" it copyrighted. This has been the case under
US law since 1978 (and applied retroactively to works created since 1976).
After that, it's up to you to specify any other terms under which you would like to allow people to copy it from you, and/or if they may then make more copies and distribute them to other people.
You can do this implicitly, of course, by (for example) instructing your web server to make a copy of your image whenever someone's browser requests it and to serve that copy to that person over the internet for the purposes of displaying it in their browser. (This, of course, does not grant them the license to make further copies.)
You can also do this explicitly: on my web page, for example, I have some software that I have written. It comes with a copyright notice and a copy of the
GNU General Public License, which explains in legal language that anyone may copy and modify it if they want as long as their changes are also open source and under the same license.
Creative Commons provides similar licenses for non-software works.
All of this is of course entirely up to the discretion of the copyright holder, based on what he or she wishes to permit.
While registering your copyright with the LOC is not strictly necessary, it does help if you plan on suing someone over a copyright violation, or if it is a musical/performance work and you plan on collecting royalties.
