Wendy Seltzer : Choosing a license for your digital art and code.

You've created a piece of electronic art, and now you want to share it with the world. Great! To help the world know how you want your art treated, you might want to give it a copyright license.

Under U.S. law, any original work "fixed in a tangible medium of expression" is copyrighted automatically, and copyright's default terms prohibit reproduction, public performance, or public display without the author's (or copyright holder's) permission, unless itŐs fair use. If you like those restrictions, you don't have to do anything (although registration can help if you want to sue someone).

But those restrictions aren't so helpful if you want others to share your work and help it spread. Attaching a permissive license to your work can let your fans (and critics) know they're free to show and re-post it, even to re-mix parts of your work in their won, to make something new.

The right license depends on your goals, your tools, and whether you're building on others' works.

If you're using pieces from others' works, you might be able to rely on fair use, but if not, you'll need to look at the license terms of those works: you can only give others the rights that are yours to give.

Fair use is an exception built in to copyright to allow use without permission for purposes including commentary, criticism, and scholarship. Unfortunately, fair use is also a very fact-specific determination, looking at factors such as the amount of the work used and the "transformative" nature of the use. (Older works might be in the public domain, completely free for re-use, but since Congress has extended copyright terms so often, most newer sources won't be.) If you don't count on fair use, you'll want to follow the terms under which the work was licensed, and include those in your own license. If you use Free Software, code licensed under the GNU GPL, for example, you must license your project under the GPL too and release its source code. If you use an artwork licensed under a Creative Commons non-commercial license, you can only license your work for non-commercial use.

If you're starting from scratch, without more than fair-use excerpts from others' code or art, your choices are open. Think about how you might want to allow others to use your work.

Do you want others to be able to re-use software code you've created? Look for an open source license commonly used by others writing in the same programming language, so it will be compatible with other code they might use. Do you want artists to be able to include your art in their creations? Creative Commons offers a series of licenses and a helpful guide to choosing one. Do you want to be able to re-use others' creations if they use your work? Pick a license with a "copyleft" or "share-alike" feature, such as the GNU GPL (for code) or CC-SA (for non-code art).

For further reference:
  Creative Commons - choose a license
  Creative Commons - list of licences<
  Free Software Foundation on licensing
  Open Source Initiative - list of open source licenses
  Chilling Effects Clearinghouse - Fair Use FAQ