The board voted to make the change effective starting with ITK version 4.0, and leave previous versions of ITK to maintain the license under which they were originally released.
The motivations to replace the BSD License with the Apache 2.0 License include
The Apache 2.0 license is a well established license in the Open Source community and has been very closely evaluated by commercial, academic and non-profit organizations.
The method for applying the license to the toolkit was also modified in order to match the recommended practices of the Apache Foundation
Following the recommended practices of the Apache Foundation
we propose to replace the current header that all ITK files have:
/*=========================================================================
Program: Insight Segmentation & Registration Toolkit
Module: itkImage.h
Language: C++
Date: $Date$
Version: $Revision$
Copyright (c) Insight Software Consortium. All rights reserved.
See ITKCopyright.txt or http://www.itk.org/HTML/Copyright.htm for details.
This software is distributed WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the above copyright notices for more information.
=========================================================================*/
with
<source lang="cpp">
/* ========================================================================= * * Copyright Insight Software Consortium * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0.txt * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. * *=========================================================================*/
</source>
<source lang="cpp">
/*========================================================================= * * Copyright Insight Software Consortium * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0.txt * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. * *=========================================================================*/ /*========================================================================= * * Portions of this file are subject to the VTK Toolkit Version 3 copyright. * * Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen * * For complete copyright, license and disclaimer of warranty information * please refer to the NOTICE file at the top of the ITK source tree. * *=========================================================================*/
</source>
The principal points in which the Apache 2.0 differs from the BSD License are listed below. Please note that this is an informal summary of the differences. You must read the full license in order to evaluate all the differences.
2. Grant of Copyright License.
Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare Derivative Works of, publicly display, publicly perform, sublicense, and distribute the Work and such Derivative Works in Source or Object form.
3. Grant of Patent License.
Subject to the terms and conditions of this License, each Contributor hereby grants to You a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable (except as stated in this section) patent license to make, have made, use, offer to sell, sell, import, and otherwise transfer the Work, where such license applies only to those patent claims licensable by such Contributor that are necessarily infringed by their Contribution(s) alone or by combination of their Contribution(s) with the Work to which such Contribution(s) was submitted. If You institute patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that the Work or a Contribution incorporated within the Work constitutes direct or contributory patent infringement, then any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed.
The Apache 2.0 License included terms indicating that developers who submit contributions to the software implicitly authorize their redistribution under the terms of the Apache 2.0 License.
Verbatim:
5. Submission of Contributions.
Unless You explicitly state otherwise, any Contribution intentionally submitted for inclusion in the Work by You to the Licensor shall be under the terms and conditions of this License, without any additional terms or conditions. Notwithstanding the above, nothing herein shall supersede or modify the terms of any separate license agreement you may have executed with Licensor regarding such Contributions.
This was already listed in the Patent terms, but it deserves to be pointed out again:
If You institute patent litigation against any entity (including a cross-claim or counterclaim in a lawsuit) alleging that the Work or a Contribution incorporated within the Work constitutes direct or contributory patent infringement, then any patent licenses granted to You under this License for that Work shall terminate as of the date such litigation is filed.