Introduction to Copyright and Licensing
Note: This is an expanded version of the Chapter “Sharing work of others: Copyright”. Here you find more details on the choice of licenses.
By default, everything you put into the project folder will be shared publicly. In many instances, this will also include works by others than yourself or your co-authors, because you may use existing data, images or software. In these cases, you should make sure to only share them to the extent you are allowed to. In the following, we will be focusing on copyright, but of course, there can also be other restrictions.
Every expression of an idea, such as a literary or an artistic works, is automatically covered by copyright. Put simply, this means that nobody else than the copyright holder is allowed to copy, modify, or share it. Copyright licenses can grant others some of the necessary rights, but mostly don’t cover publicity, privacy, moral, patent, or trademark rights. Certain exceptions and limitations to copyright (such as fair use or the right to quote) may obviate the need for a license.
With regard to copyright, free/open licenses can give permission to share a work by others. These licenses often require to attribute the authors, indicate whether changes were made, and provide the text of the license, among other things.
The following video by Brinken et al. (2021) embedded from the TIB AV-Portal (Data Privacy Statement) explains the correct attribution of works under Creative Commons licenses.
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The video “The correct indication of a license: Aspects to consider when reusing the work of others” by Helene Brinken, Jonas Hauss, and Jessika Rücknagel is licensed under CC BY 3.0 DE.
Introduction to Copyright and Licenses
Whenever authors create a literary or artistic work (such as a text, image, video, or software), the copyright law1 in most countries limits other people from copying, modifying, and sharing it without the author’s express permission. This even applies if the author makes it available to others (e.g., on their website): First and foremost others are not allowed to copy, modify, or share it. Importantly, this legal default of “all rights reserved” was created to benefit publishers, not authors (Fogel, 2006), and runs counter to many cultural and scientific processes. Copyright licenses enable authors to free up their works for reuse by others.
Note that copyright law varies between countries and the rule of territoriality (lex loci protectionis) applies: Applicable are the laws of the country where a work is used. Also, if the work was created as part of the author’s job, it might be their employer who holds the copyright to the work, depending on the country and contract.
A license is a legal document that regulates what other people than the author can and cannot do with a copyright-protected work, and under which conditions. The license may be exclusive, such that it is only granted to one recipient, effectively limiting the author in dealing with their own work. It can also be non-exclusive, thus giving rights to others without the author losing them. To avoid that every author who would like to share their work writes their own license, pre-formulated “boilerplate” licenses have been created. For example, you might have heard about “Creative Commons” licenses, which are used by Wikipedia. Recognizing them facilitates both sharing (on the side of the author) and re-using (on the side of the recipient).2
For the purpose of this tutorial, by license we mean copyright license.
An important class of boilerplate licenses are free/open licenses. Put simply, works under a free/open license “can be freely studied, applied, copied and/or modified, by anyone, for any purpose” (Möller et al., 2015). Importantly, this also means that others do not need to ask or notify the author and that they can use it for commercial purposes. Coming back to the example of Creative Commons licenses, not all of them are free/open. For example, some restrict commercial use and modification. The Creative Commons license “Attribution-ShareAlike 4.0” is an example of a free/open license, however, and we will cover several others below.
By the choice of license, authors can demand that they are credited, that the original license is indicated, that modifications are indicated, that derivative works are only shared under the same license, and that no further restrictions are imposed on the work. Software licenses may additionally require to make the source code available to everybody the software is shared with and often require to display the full text of the license upon distribution.
The terms free and open, especially with regard to software, come with a history. The Free Software Foundation (FSF) was founded in 1985 to protect “four essential freedoms” (2024) of a program’s user. These are the freedoms to use, study, share, and improve a program. Software whose users legally and practically have these freedoms (because, among other things, they have access to its source code) is considered free. The four freedoms are seen as vital for a society as a whole in the sense that they enable sharing, cooperation and ultimately freedom in general. The FSF maintains a list of software licenses that it considers to be protecting the four freedoms. Sometimes the term libre (Spanish and French for free) is used to make a distinction from gratis software. You can learn more about free software at Write Free Software.
The Open Source Initiative (OSI), which was founded in 1998, follows a more pragmatic approach. It is concerned with developing high-quality software, for which everyone’s ability to obtain, modify and contribute back the source code is considered beneficial. Access to the source code is one out of multiple conditions for software to be considered open source by the OSI (2007), which equally maintains a list of approved licenses.
Access to the source code is a necessary, but not sufficient requirement both for free software and for open source software. Conversely, both can (and frequently are) sold for money, as their respective criteria only apply once one has access to the software. Throughout this tutorial, we write “free/open license” to mean a license that is approved by either the FSF or the OSI. Software which is neither but makes available its source code is sometimes referred to as source-available software.
Apart from software, the term open access has often been used for works that are available at no cost. For example, this is the commonality of bronze, green, hybrid, gold, and diamond/platinum open access articles, which otherwise vary in the rights that are granted to readers. In 2002, the Budapest Open Access Initiative declared that open access additionally includes the right to use articles for any purpose, and in 2003, the Bethesda Statement and the Berlin Declaration added the right to make derivative works.
Two other notable definitions include the Open Definition (Open Knowledge Foundation, 2016), which was first drafted in 2005, and the definition of Free Cultural Works (Möller et al., 2015), for which the open editing phase began in 2006. They are largely viewed as compatible with one another.
Under Which Conditions?
Finally, if you verified that the work has been made available to you under a free/open license, you need to understand the conditions under which you are allowed to include the work in your project folder and share it with others – regardless of whether you modified it. In the following, we will explain the most important conditions of the licenses listed above. For other licenses we recommend reading their text in full and/or consulting with a lawyer. The conditions of many popular free/open licenses are also summarized on ChooseALicense.com, which you can use to get a general idea of a license (but which does not obviate reading the license text in full). Specifically for software licenses the Open Source Automation Development Lab provides useful checklists detailing the respective obligations.5
In the following, we only discuss the conditions under which works may be shared. This is because free/open licenses put no conditions on private use, where the work is not made available to others.
Attribution
Licenses may require that you provide attribution to the author(s)6 and to retain any copyright notices,7 although the specifics vary between licenses. For example, Creative Commons licenses other than CC0 require that the name of the author, the title of the work, and a link to the work are provided.
Projects with many authors often explicitly allow for an attribution to the collective as a whole rather than being mentioned individually. For example, the flexible attribution requirements of Creative Commons licenses allow that Wikipedia authors agree to be attributed through a link to the article (Linksvayer, 2009). And software projects may use copyright notices that only contain the project name, such as Copyright (c) 2020-2025 The XYZ Project Contributors (Winslow, 2020).
Where to put the attribution depends on the type of the work, but in general it is best to keep it close to where the work is used and to provide all required information. Only linking to a page that provides the attribution (as with Wikipedia articles) most likely will not suffice in general.
State Changes
If a work has been modified, licenses may require that this is indicated. For example, if an image under a Creative Commons license other than CC0 is reused in a cropped version, reusers could add “adapted from original” to indicate that changes have occurred.
Indicate License / Add License Text
Licenses may either require that one mentions the applicable license by name and possibly link (“Indicate license”) or they even require to copy the full license text along with the used work (“Add license text”). Of course, the latter may not be feasible if the work is printed and smaller than the license text. For example, if the license of an image requires to print the full license text, the image mostly cannot be used in newspapers (see Wikipedia contributors, 2025).
Disclose Code
There are various situations in which one interacts with software without having access to the underlying source code. For example, software can be distributed as a binary (“executable”) file or it can be used over the internet. In both cases, licenses may require that the source code is provided to its users.
Anti-DRM
You may have encountered images or videos which you could not download due to a copy protection. Such a protection is also called digital rights management (DRM). For works published under a license with an anti-DRM clause, reusers may not apply DRM to the work or must provide a DRM-free version in parallel (depending on the exact license).
Copyleft
If you modified the work and put a sufficient amount of creativity into it, the result is called a derivative work. It is (again) protected by copyright and even if you share it, nobody except you is allowed to copy, modify, or distribute it further. You can put it under a free/open license but don’t have to.8 The only exception is if the original work has been made available under a “copyleft” license. In that case, if you share the work with others you must put it under the same license as the original work9 – or you commit a copyright violation.10 This explains the origin of the term copyleft, as it “turns copyright around” to make works permanently free: © → 🄯. In the realm of Creative Commons licenses, copyleft is also called share alike. The opposite of a copyleft license is sometimes also called a permissive license.
What is considered creation of a derivative work varies between jurisdictions, but the following are typical examples: translating a text into a different language, taking a picture of an artwork, adding a song to a video, adapting a computer program to fit own use cases, or taking a screenshot of a computer program. In all of these cases, if the original work is under a copyleft license, then sharing of the resulting derivative work is only allowed if it is put under the same license.
The question is then: Which uses of a work do not create a derivative work? In many cases, if an unaltered excerpt “is used to illuminate an idea or provide an example in another larger work” (Creative Commons, 2024a) no derivative work is made. The excerpt needs to “remain separate and distinct in the new context” (Kreutzer, 2024, p. 44) and not be “merged with other material into a new and larger work” (Kreutzer, 2024, p. 45). For example, embedding images in a document and clearly separating them from the rest or assembling works as part of a collection typically would not create a derivative work. However, due to a lack of case law, there is only little guidance on what constitutes a derivative work in general.
Also note that the copyleft licenses we discuss here do not mandate sharing. Copyleft (and attribution) clauses are only triggered if the work is shared (Creative Commons, 2015). This means that if you only use a work internally, you do not need to share your derivative works.
For software, copyleft licenses come in two flavors:
- Weak copyleft licenses only require that modifications to the software itself are licensed under the same or a compatible license if shared. For example, if you create and publish software under a weak copyleft license, others who modify it and put their version on the internet have to apply the same license. However, people who merely use your software in their own work which they make publicly available can choose any license for it.
- Strong copyleft licenses, on the other side, insist that any larger works that use the copyleft-licensed software must also be licensed under the same or a compatible license if shared. For example, if your software were to be put under a strong copyleft license, everybody publishing software that uses your software would need to put it under the same license. Because of only few rulings in courts, the extent of this requirement is disputed (Wikipedia contributors, 2024).
Further Remarks
The description of the conditions above is a simplified summary – read the full text of the license before sharing the respective work with others. For example, Creative Commons licenses other than CC0 also require that
- you retain a notice about the disclaimer of warranties,
- you retain an indication of any previous modifications,
- the attribution does not imply endorsement by the original author, and
- you remove the attribution again upon request by the original author.
For most Creative Commons licenses, providing the following information is required (if available):
Obviously, if you are in doubt whether a condition of the license applies in your use case, it is better to either follow it or to ask the author for clarification or explicit permission. This is especially important given the existence of copyleft trolls: People who distribute works under a free/open license but send out statutory damages claims after minor violations without providing reusers an opportunity to fix their error. In addition, in many European countries attribution may be necessary regardless due to the author’s moral rights. For these reasons, we recommend that you provide attribution for all works under a free/open license – even if the license does not strictly require it (e.g., CC0). Also, you should take note of every foreign work included in your project folder and record its license.
The free/open licenses we discuss here mostly grant copyrights (with some of them explicitly granting patent rights and sui generis database rights). Therefore, you may lack other rights such as personality, privacy, moral, or trademark rights. For example, sharing photos that depict people is not only a matter of copyright, but also of privacy rights. Also, their commercial use may require the consent of the depicted person. Finally, note that even if attribution is not a requirement of the license, good scientific practice demands that appropriate citations are made.
Wrap-up
If you would like to learn more about copyright and licenses you might find the following resources interesting:
- “Open Content – A Practical Guide to Using Creative Commons Licences” by Kreutzer (2024)
- “Creative Commons Certificate for Educators, Academic Librarians, and Open Culture” by Creative Commons (2024b)
- “Freie Software – Zwischen Privat- und Gemeineigentum” by Grassmuck (2004)
- “Rechtsfragen bei Open Science: Ein Leitfaden” by Kreutzer & Lahmann (2021)
References
Footnotes
in Germany: Urheberrecht↩︎
In fact, authors should not create their own license texts if the purpose is to share their work freely and openly with others. By using a boilerplate license others know what to expect, also because it may have already been tested in courts.↩︎
in Germany: Gemeinfreiheit↩︎
in Germany: Schranken des Urheberrechts↩︎
Accessing the checklists requires a (free) account on their website.↩︎
or others whose names are provided with the original work↩︎
Such as
Copyright (c) 2025 Jane Doe↩︎Of course, you still need to abide by the license conditions of the original work, such as attribution.↩︎
or sometimes also under a later version or under a compatible license↩︎
Note, however, that copyleft licenses are not automatic: A derivative work of a copylefted work is not “implicitly” under the same license – others would commit a copyright violation if they just took it. Only if the derivative author explicitly makes it available under the same license, others may use the derivative work under the same terms.↩︎