Content licensing schemes can range from individual licenses drawn up by corporate lawyers to govern the sale and use of software and websites, to open “copyleft” licenses which are intended to do precisely the opposite. Copyleft licenses promote open content creation as they prevent derivative works from becoming proprietary through integration of source material with a proprietary license.
“Copyleft is a play on the word copyright to describe the practice of using copyright law to offer the right to distribute copies and modified versions of a work and requiring that the same rights be preserved in modified versions of the work. In other words, copyleft is a general method for making a program (or other work) free (libre), and requiring all modified and extended versions of the program to be free as well.” (From Wikipedia)
Copyleft licenses may run into problems when people attempt to combine copyleft content with any other content – even if that content is already under an open license. If materials under different licenses are used in a product, the strictest license prevails. So copyleft licenses would impose more restrictions when combined with works under a more open license, such as public domain works or Creative Commons 0. In many cases, the licenses may not be cross-compatible at all. Some open licenses attempt to preemptively address this problem by restricting which licensing agreements they may be combined with.
- For an interesting example of an open licensing scheme, check out Wikimedia Commons. Wikimedia Commons made a revolutionary step when it released a comprehensive system for licensing and tagging media works in order to generate a commons of accessible material. The site presents a clear breakdown of various copyright regulations from over 100 countries, including which works fall into public domain (and when). In addition, they have compiled a list of all the licenses under which a work can be released while remaining open and free for downstream users. I look under the hood of their licensing scheme in New Global Content Commons? Thanks, Wikimedia.↵