"BABY Got Back" is an exuberant hip-hop paean to female callipygian bounty. Neither subtle nor refined in its appreciation thereof, it has nonetheless remained popular thanks to its catchy tune and clever but ribald lyrics. In September 2005 Jonathan Coulton, a musician then developing a reputation among internet geeks, quit his day job as a programmer and began releasing one song a week over the subsequent 12 months. His fifth was a folk-rock acoustic banjo ballad cover of Sir Mix-A-Lot's 1992 classic. Even as Mr Coulton's career has burgeoned, that tongue-in-cheek rendition remains one of his best-known songs. It is a frequent request when he performs on television, as a musical sidekick on a quiz show aired on America's National Public Radio or on one of his regular tours or "JoCo" cruises (600 fans have booked passage for the next one on February 10th-17th). Still, it came as something of a surprise when Mr Coulton got wind that a near-identical version of his cover might appear with new vocals on "Glee", a popular television show about a high-school choir group. And so it did, in an episode which aired on January 24th. The show's songsmiths create remarkable choir reworkings of classic and modern popular songs. However, once scrubbed of the singers, the song as played on "Glee" sounds remarkably similar to Mr Coulton's recording. Paul Lamere created side-by-side versions that alternate by beat between Mr Coulton's and Fox's renderings. Paul Potts performed waveform comparisons of the two tracks and found that the "Glee" track even contains a telltale trace of a duck quacking, which Mr Coulton inserted in his cover rather than speak the song's original obscenity. Mr Coulton says that when he examined that vestigial quack from "Glee" using his own audio software and boosted the volume, it was identical to his source material.

Predictably, Twitter erupted with ire towards "Glee" for appropriating Mr Coulton's work without advance notice, permission or credit. The internet's socially connected participants regularly embrace mash-up culture, in which unrelated songs or video are transformed into new works that transcend the original. But the same people reject outright appropriation unless the creator explicitly authorises it.

While much of Mr Coulton's music is released under a Creative Commons licence that allows non-commercial re-use with attribution, "Glee" is patently commercial and omitted his name in the credits. But unless it turns out that Mr Coulton's audio was indeed appropriated, in which case his specific recording is protected by a so-called phonogram right, the show's producer and network, Fox (which declined to comment for this article), may have had no legal obligation to do so. The rights to the composition, Mr Coulton's and others' possible covers notwithstanding, belong to Anthony Ray, as Sir Mix-A-Lot is known off stage.

Indeed, in creating his cover version, Mr Coulton relied on the principle of international copyright law known as "compulsory licence". America's reading of it, as defined in law and applied to musical works, accords the privilege of a first recording to the owner of the original composition. But once that recording is fixed in a medium (CD, digital, vinyl, etc) and released to the public for sale, rental, lease or lending, any performer may create new audio recordings without obtaining permission. The relevant section of the American legal code stipulates the conditions crooners must meet:

A compulsory licence includes the privilege of making a musical arrangement of the work to the extent necessary to conform it to the style or manner of interpretation of the performance involved, but the arrangement shall not change the basic melody or fundamental character of the work, and shall not be subject to protection as a derivative work under this title, except with the express consent of the copyright owner.

An artist must notify the composition's current copyright holder either before recording or within 30 days of it, but before any copies are distributed. He must also pay a royalty set by a trio of copyright judges for each copy sold or distributed. The going rate is 9.1¢ for songs five minutes or shorter, and 1.75¢ per minute over five minutes—not to be sniffed at in an era of 99¢ digital music.

When Mr Coulton created his arrangement of "Baby Got Back", he contacted Harry Fox Agency, a major rights manager unrelated to the Fox media empire, and has paid the royalty fee as required. Compulsory licence includes only sound recordings, however, and, as the code makes clear, does not protect cover versions separately from the original composition.

John Bergmayer, an attorney specialising in intellectual property at the non-profit Public Knowledge group, says that Fox might have any of a number of standing relationships with specific record labels or with rights clearing houses like ASCAP, SESAC or BMI. This, probably combined with a portfolio of copyright permissions to record and televise a performance called a sync licence, would have granted it the right to perform, air and later release DVDs and CDs of the song.

Mr Ray has at least some of his rights handled by Harry Fox, but would have been alerted and given a right of refusal, although probably without specific knowledge of the show's arrangement. Some bands, including Kings of Leon and Foo Fighters, have either turned "Glee" down or pre-emptively forsworn any dealings with the show.

In many markets outside the United States, Mr Coulton could insist that Fox respect his "moral rights" to the arrangement. These can vest irrevocable, non-monetary privileges to a creator. Across Europe, for instance, moral rights allow an artist to block reproduction, modification or dissemination of a work that lacks attribution (or provides attribution when the original author chooses not be identified). But moral rights are absent from the American legal lexicon.

For now, then, Mr Coulton is examining his options and his lawyers have spoken with Fox. He thinks the kerfuffle is unlikely to boost his revenues substantially through publicity, partly because he is not named in the broadcast. Even if the concomitant outcry did work to his advantage, this is little consolation for what he describes as a misuse of his work—particularly jarring because "Glee" claims to champion precisely the sort of independent underdog Mr Coulton represents. Still, he is using the little bit of extra attention to release what he calls a cover of Glee's cover of his cover of Sir Mix-A-Lot's song—ie, his original recording, which quickly rose into iTunes's current top 200 songs chart. Any profits will go to charity.