Licensing of the Orthanc ecosystem ¶

Contents

Licensing of the Orthanc ecosystem

Philosophy ¶

The objectives of the Orthanc ecosystem is to share technical knowledge about DICOM, to build a consistent platform for developing medical imaging software, and to foster scientific collaborations in medical imaging by subscribing to the open-science paradigm. To this end, Orthanc is provided as free and open-source software to the benefit of the worldwide community of medical imaging.

In order to support this objective of global knowledge sharing, the Orthanc project enforces reciprocity. If someone finds Orthanc useful to her academic work or to her business, the community of medical imaging should gain an advantage from this use by enlarging the knowledge base. This virtuous circle guarantees the fact that Orthanc will be developed in a sustainable way in the long-term, to the benefit of all stakeholders. Predatory behaviors should be prevented, while preserving the freedoms of the users of Orthanc, including the commercial uses.

According to this philosophy, the University Hospital of Liège decided to release the Orthanc ecosystem under the GPLv3+ license in 2012. The GPL is a strong copyleft license that is recognized worldwide, and that is designed to enforce reciprocity.

As Orthanc is lightweight and designed for Web applications and for sharing medical images over Internet, it has been quickly deployed on cloud platforms in order to host large amount of data. Orthanc considers this use as very legitimate, for instance for scientific purpose (think of open-data databases) or for societal needs (think of teleradiology platforms in developing countries). Unfortunately, the GPL does not protect from predatory commercial behaviors over cloud platforms because of the so-called “ASP loophole”, that does not enforce derived versions of a free and open-source software running on a server to be given back to the community.

For this reason, the plugins that provide scalability-related or cloud-related features (for instance the PostgreSQL and Web viewer plugins that are necessary for Web applications distributed at a large scale) were released under the stronger AGPLv3+ license. This license protects the community of medical imaging by ensuring that the features included in Orthanc instances running in remote servers are publicly available as well.

The intellectual property over the source code of the Orthanc project is now shared by the following entities:

University Hospital of Liège, from 2012 to 2016.
Osimis S.A. that has unfortunately ceased to exist at the end of January 2024, from 2017 to 2024.
Orthanc Team SRL, starting 2024.
UCLouvain university, starting 2021. UCLouvain contributions since September 1st, 2021 are 100% owned by UCLouvain and made available to the benefit of the free and open-source community. No dual licensing is possible on those contributions.

Together, these entities act as the official guardians of the whole Orthanc ecosystem. New intellectual property is currently added by the following entities:

Orthanc Team SRL.
UCLouvain university.
Various individual contributors.

Guidelines ¶

Over the years, it was observed that people fear the use of GPL and AGPL licenses, that are wrongly considered as preventing commercial uses. This is most often a wrong assumption, given that the Orthanc server is a standalone executable, not a software library.

The following table provides a simple summary of the most common situations, and indicates whether the use is accepted (“Yes”), forbidden (“No”), or restricted:

		Mode of distribution of the third-party system, or of the third-party plugin/script
Usage of the Orthanc ecosystem		Permissive (MIT, BSD, Apache…)	GPLv3	AGPLv3	Internal use	Proprietary software distributed to clients	Proprietary cloud platform or Web portal
Using Orthanc as such, even if some AGPL-licensed plugin is installed		N/A	N/A	N/A	Yes	Yes	Yes
Calling Orthanc from a third-party system (using REST API or DICOM protocol), even if some AGPL-licensed plugin is installed		Yes	Yes	Yes	Yes	Yes	Yes
Creating a C/C++ plugin, creating a Lua script, creating a Python plugin, or creating a Java plugin. 2 possible cases:
	Case 1: No AGPL-licensed plugin is in use	No	Yes	Yes	Yes	Restricted	Yes
	Case 2: Some AGPL-licensed plugin is in use	No	Yes	Yes	Yes	Restricted	Restricted
Using a derived version of the GPL-licensed code of Orthanc, or using a derived version of some GPL-licensed plugin, or reusing their original code in a third-party system		No	Yes	Yes	Yes	Restricted	Yes
Using a derived version of some AGPL-licensed plugin, or reusing its original code in a third-party system		No	No	Yes	Yes	Restricted	Restricted
For viewers: Using a derived version of the Orthanc Web Viewer, of the Osimis Web Viewer, of the Stone Web Viewer, or of the sample applications of Stone of Orthanc (AGPL license)		No	No	Yes	Yes	Restricted	Restricted

Notes:

The wording “third-party system” is very broad, as it encompasses many possibilities. It can for instance be a Web application, a heavyweight desktop application, an automated script, or more generally any system that takes advantage of Orthanc as a service in its global architecture.
If you reuse code from Orthanc or one of its associated plugins, you must mention the copyright of the Orthanc project.
An Orthanc plugin cannot be licensed under a permissive license (MIT, BSD, Apache…) because it cannot run independently of the Orthanc SDK, which implies that the plugin and the Orthanc core form a single combined program, which in turn means that the plugin should be licensed under GPLv3 by copyleft contamination. Check out the license compatibility matrix on Wikipedia. Here is the corresponding entry about this topic in the GPL FAQ: “If the main program dynamically links plug-ins, and they make function calls to each other and share data structures, we believe they form a single combined program, which must be treated as an extension of both the main program and the plug-ins. […] If the main program and the plugins are a single combined program then this means you must license the plug-in under the GPL or a GPL-compatible free software license and distribute it with source code in a GPL-compliant way.”
You are kindly invited to cite the reference paper about Orthanc in your scientific work.
This is our own simplified, technical interpretation of the GPLv3+ and AGPLv3+ in the very specific context of Orthanc. It is not intended to be a complete guide to copyleft licensing. Please get in touch with the Free Software Foundation for more legal information.

Restricted uses ¶

If your use case falls in a “Restricted” cell, this means that your third-party system must change its license to GPLv3 (or AGPLv3 if some AGPL-licensed plugin is in use).

In the past, it has been possible to buy dual licenses from the Osimis company, that was the only entity entitled to grant a license exception to your company for the Orthanc core and its associated official plugins. Nowadays, dual licensing is no longer available and never will be again on any version of Orthanc that ships code owned by UCLouvain.

In particular, the latest version of the Orthanc server that could be eligible for dual licensing is Orthanc 1.9.7 that was released on 2021-08-31. All the subsequent releases of Orthanc contain code owned by UCLouvain.

Contributing to the code of Orthanc ¶

Contributed vs. internal code ¶

It is important to make the distinction between contributed code and internal code:

Contributed code refers to source code that takes advantage of Orthanc and/or that extends Orthanc, such as new plugins, Lua scripts, or any higher-level application that uses the REST API of Orthanc. This code can live outside of the official source repositories of the Orthanc ecosystem. External contributors can distribute such contributed code on whatever platform they prefer, in a way that is fully uncoupled from the Orthanc project, and keep the intellectual property of their developments. Such contributors are however kindly invited to index their contributions in the dedicated repository on GitHub, and contributed plugins should also be indexed in the Orthanc Book.
Internal code refers to source code that only makes sense if embedded within the Orthanc core or within one of the official plugins. This includes new features and bug fixes. The way to contribute to the internal code of the Orthanc ecosystem is described in the sections below.

Important: You should always favor the creation of a new plugin over modifications to the internal code of the Orthanc ecosystem if your intellectual property is of importance to you.

Contributor License Agreement ¶

Until the end of January 2024, before any code could be accepted into the official repositories of Orthanc, the individual code contributors had to sign a Contributor License Agreement (CLA) to transfer their intellectual property to the Osimis company.

Starting February 2024, no contributor license agreement is needed to submit code to the Orthanc project anymore.

Submitting code ¶

To submit code to the Orthanc project, use Mercurial to fork the official repository of interest. All the repositories are centralized on our self-hosted Mercurial server.

A dedicated page explains how to submit simple patches or full branches.

Some words of warning:

It is your responsibility to make sure that you have the intellectual property over all the source code you commit into Orthanc.
In the case of a doubt wrt. a potential contribution, please discuss it on the Orthanc Users discussion forum discussion group before starting the actual development.
The Orthanc project follows high standards of quality. Beware that your contributions will be rejected if they do not meet our standards.