Related to this question on libertarianism on monopolies, how do libertarians in the USA, as represented by the Libertarian Party, view copyright and patent protections?
A useful litmus test on whether a right is natural or artificial is to consider the right in the absence of a state. Would a society recognize that right if there were no state compelling them to? Could that right be practically enforced in the absence of a state?
With commonly accepted natural rights such as the right to life and the right to property the answers to both these questions is an unqualified "yes". Even before the development of private property (land) around 12000 BC-10000 BC there is a consensus among historians and anthropologists that humans recognized personal property. With intellectual property this is far less likely. To this day a large percentage of the population routinely ignores intellectual property law whenever the opportunity arises.
Without a state could an inventor or content creator insist intellectual property rights be included in contractual arrangements with distributors and retailers of his product? Sure. The question is what incentive would those parties have to engage in such a contract if there are other creative persons who make no such demands?
Of course to have the same reach of the state, any such contract would need to be viral in nature. By which I mean it would need to bind consumers beyond the first sale in perpetuity. Otherwise, even if distributors and retailers agreed to the contract, the consumer, as a third party, would be under no obligation to abide by it.
Contrast this with private property, which has both widespread acceptance and requires little more than a willingness to use force to defend it against trespass.
As for whether the tenets of libertarianism support intellectual property one need only compare intellectual property with those tenets.
Intellectual property assumes the inventor/creator has the right to control the use of his idea by others. This is at odds with the notion of self-ownership. If individuals are self-owners then the individual has a sole and exclusive right to his own mind and body and by extension, his own actions unless those actions violate the equal rights of other individuals. To claim that the act of copying and/or improving upon someone else's ideas is a violation of that person's rights you would first need to establish that their original creative act resulted in a natural right to prevent others from doing so. This is a tenuous argument at best.