Copyrighting material in some countries is unnecessary and also not possible. For example, in England, something is copyrighted as soon as it is on paper or some other medium. In the United States, music is copyrighted as soon as it is recorded. Proving copyright infringement is another matter. The United States government allows for formal registering of copyrights, of any artistic creations, with a government institution called the Library of Congress. International copyright agreements give you protection in other countries as well when registering with the Library of Congress.
A less formal option is a poor man’s copyright, where you place a recording or a piece of sheet music into an envelope and mail it to yourself. You physically send it through the mail and get the post office to clearly frank the envelope. When the envelope is delivered, do not open it. However, a poor man’s copyright can be faked because one can also steam open envelopes and change their contents. The real benefit to using a Library of Congress copyright, as opposed to a poor man’s copyright, is as follows: if someone does copy one of your songs, a Library of Congress copyright will help the strength of your case in a courtroom. Unfortunately, in America, the law is often in the hands of those who can afford the most expensive lawyers, unless of course you have a rock-solid case. So, a Library of Congress copyright is always the most prudent way to protect yourself. You can even copyright batches of songs on a single CD, protecting all of your words, melodies, and even the sound recording of the arrangement as a whole.
Copyright your stuff! Infringement is rare because it can cost the perpetrator dearly. Copyright infringement can even be criminally prosecuted in the United States under federal law.
As a songwriter you have the strongest protection if you copyright properly. Don’t ever be afraid of putting your stuff out there. If it’s not out there nobody but you will ever hear it. Yes, people can cover your songs but technically only if you publish them somewhere like ASCAP or the Harry Fox agency. If someone does copy you, and they make money, then you will as well. If you don’t get a cut, then you can get compensation under civil law. Additionally, copyright can be punishable under criminal law. So quit worrying about people copying your stuff! If some famous person copies your song, makes a mint, and you can prove it, any lawyer with dollars in his eyes will be willing to negotiate a cut for you (and for himself of course), assuming you have a strong case (a provable copyright).
One more thing, playing your songs in a band gives the band some rights to your songs, but only to play them, probably not to record them if you have already written, arranged, copyrighted, recorded, and released them on CD. Typically, if you look at CDs you may find that individual songwriters are listed as writers of specific songs, with arrangements and instrumentation listed separately. There are exceptions of course such as Lennon & McCartney writing all Beatles songs equally—in reality probably only partially true. Also, I find that not allowing any other band member to take the lead vocals role from you as the songwriter is another way to ensure that the band does not continue playing your songs if you leave. Unless of course you write the songs with that band, everyone contributes, all are interested in performing your stuff and they don’t make unfair claims to anything they didn’t create. Credit where credit is due! There are even stories of people handing off small percentages of their copyrights to people like producers and recording engineers. This is often unnecessary and can occasionally wind up costing the artist a small fortune.
In general, only words and music are copyrightable. What that means is that lyrics and melodies are copyrightable, implying that any instrumentation or arrangement is not included in a copyright unless it’s a fundamental part of a song. So drums and riffs on a lead instrument, unless they distinctively define the song, are not copyrightable. The song Sweet Child of Mine by the band called Guns And Roses has a distinctive lead guitar part, which is probably copyrightable because it defines the song. Chord progressions for example are not copyrightable in any way, state or form; no exceptions! For example, the guitar parts in the Beatles song Here Comes the Sun might be copyrightable from the perspective that the guitar picking follows the melody and in the melody in some respects; but the chord progression itself is probably not be copyrightable.
I was told recently that it takes talent to create but genius to copy. There is one songwriting method that involves taking an already written melody and changing a few keys here and there to come with an equally good melody, resulting in a new song; perhaps even a better melody. I have tried this method a few times and what I come up with usually comes out worse or just sounding like the original one written by someone else. Of course if the original composer’s copyright has expired then it doesn’t matter, except to purists. Try listening to a piece of music by Bach called Air on G-String; and then go and listen to Procul Harum’s A Whiter Shade of Pale – there is a striking similarity but both are strokes of genius perhaps. However, be warned that trying to create the latest alternative rock hit from Mozart’s Serenade for Winds would be complete folly and might be akin to trying to put round pegs into square holes. So don’t try too hard to search for new melodies where nothing so complex is really required; modern music has words as well as instrumentation and often the instrumentation is only supporting the central lyrical theme.
There is one obvious additional danger in using another piece of music and changing a few bits here and there to come up with a new song – maybe the previous composer did the same thing and you might by fluke or subconscious error wind up with the same melody as the first composition. Now if you were a classical composer copying a baroque composer then that’s just cool – but if you are a modern-day pop songwriter varying on a theme from another pop music songwriter, suffice it to say that you might wind-up getting your nuts in a tangle, or your tits in a tangle, depending on your sex of course 
Furthermore, copying something to make something else is fine as long as you don’t arrive at something that someone else has copyrighted, before it was copied and changed by the song you changed it from. *shrug* The one thing I find myself doing is melody copying my own melodies – if I ever changed someone else’s melody on one of those I’d probably be in deep doo-doo but I do admit to trying to copy classical composers but I found that a complete waste of time and energy as classical melodies have no lyrics or are simply far too complex melodically for modern day radio pop music. Opera has lyrical content but operatic compositions of old are meant for the stage but opera is more dramatic lyrically and not too conversational. If you’ve ever been to an opera sung and written in some language you know zippo about, and found you have been moved by the performance, you will know what I mean But converting opera to pop music might be a bit of a waste of time as well.
