There are four primary types of attribution:
- Theme itself,
- Incorporated code,
- Bundled resources.
For works licensed under (or compatibly with) GPL, this attribution is important, because it ensures that end users know their rights regarding modification and distribution of the copyrighted work.
- Theme Copyright Attribution
Fred WordPress Theme, Copyright 2012 Joe Smith Fred is distributed under the terms of the GNU GPL
The Theme itself is a copyrighted work, and requires copyright attribution. According to GNU (the maintainer of the GPL):
The statement of copying permission:
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see < http://www.gnu.org/licenses/ >.
- Derivative Themes and Incorporated Code Copyright Attribution
Themes that are derived from other Themes (such as Twenty Twelve or Underscores) must declare that they are derived from another work, and include the original copyright notice from that work. For derivative works, the declaration would follow the Theme’s own copyright notice, and would take a form similar to the following:
Ginger WordPress Theme is derived from Fred WordPress Theme, Copyright 2012 Joe Smith Fred WordPress Theme is distributed under the terms of the GNU GPL
- Incorporated Code Copyright Attribution
Themes that incorporate code from other Themes (or Plugins) must declare that they incorporate code from another Theme/Plugin.
The Theme readme (or license) file should include a declaration of incorporated code:
Ginger WordPress Theme incorporates code from Fred WordPress Theme, Copyright 2012 Joe Smith Fred WordPress Theme is distributed under the terms of the GNU GPL
- Bundled Resource Copyright Attribution
Themes that bundle third-party resources (such as script libraries, PHP or CSS frameworks, images, fonts, etc.) must declare that they bundle those resources.
Ginger WordPress Theme bundles the following third-party resources: Genericons icon font, Copyright 2013 Automattic Genericons are licensed under the terms of the GNU GPL, Version 2 (or later) Source: http://www.genericons.com Cycle2 jQuery library, Copyright 2012 M. Alsup Cycle2 is dual-licensed under the terms of the GNU GPL, Version 2, and the MIT license Source: http://jquery.malsup.com/cycle2/