Many hobby pianists are looking for free popular piano sheet music online, and I wanted to explore the issue with key-notes readers.
Nearly all the downloadable sheet music in standard notation is scanned from published editions. Since most music that is currently popular is still under copyright, scanning and publishing this music online for free download is both illegal and exceedingly risky, as you'll discover below.
Tablature is worse in that it is generally offered for sale, which means persons other than the actual copyright owner are profiting from selling the sheet music. The penalties for doing so are severe, since such action is treated as a criminal offense in the United States and many other countries.
Those creating tablature often claim that they transcribed (wrote down) the music by listening to recordings of it, and that they therefore have the right to sell it. However, this argument turns out to be a misguided one. If you listened to an audiobook version of the latest Harry Potter novel and wrote it down word for word, would you then "own" that novel? Of course you wouldn't be the copyright owner—J. K. Rowling owns her work because she wrote it.
The argument that transcribing copyrighted songs is "original" work and that the transcriber therefore has the right to sell it is akin to a software hacker claiming that he may sell illegal copies of copyrighted software because he "cracked" it after all, and cracking it was "his" work. Music copyright law is extremely clear on this issue and there are no ambiguities.
Section 106, subsection 2 of the United States Copyright Law states that the owner of a copyrighted work has the exclusive right "to prepare derivative works based on the copyrighted works," where "derivative work" is defined (by Section 101) as "a work based upon one or more pre-existing works." This section then goes on to classify musical arrangements as derivative works.
Penalties for infringing sheet music copyrights in the United States are severe. If a court ruled that a copyright infringement were more or less an "innocent mistake," damages per copyright infringed would range from $750 to $30,000.
If the infringer profited from the infringed work (i.e., sold it), criminal fines of up to a quarter of a million dollars and/or up to five years imprisonment may be imposed. Again, this is per copyright infringed. Those running tablature or free sheet music download sites are therefore taking an enormous risk, and clearly the risk is just not worth it.
If you're looking for free popular piano sheet music online and download free sheet music from any of these sites, you should be aware that the owners of these sites are being paid indirectly, usually in the form of advertising. The more these sites are used, the more valuable they become to advertisers and hence the more money they make through illegitimate means.
As a classical musician I'm aware of just how seriously copyrights are taken in this business. Anyone who shows up at a music competition with photocopied sheet music is often thrown out, no questions asked!
So what's the solution? I think the best solution is to learn how to write down your favorite music yourself. It's remarkably good ear training, since you'll be learning harmony in addition to playing the melody.
It's true that it will be a difficult task at first. However, it's possible to solve the harmonic problems by learning step by step, starting with the most basic chords and gradually added more harmonies to your repertoire. You'll be surprised at how fast you learn and how much you improve as a musician!