Copyright
Most of the material you can find on the Internet is copyright – it belongs to someone and you need their permission before you can copy or change it.
Public Domain
Material in the public domain can be copied or changed without any restrictions.
Material becomes public domain either:
- when the copyright owner allows it
- or when the copyright has expired. Note that the duration of copyright varies from country to country – what is in the public domain in one country may still be copyright in another.
Creative Commons
Creative Commons is a not-for-profit organisation that provides simple copyright licenses: http://creativecommons.org/licenses/
All creative commons licenses require that you attribute the work – ie give credit to the copyright holder. Some licences allow you to modify the image, some do not allow modifications.