浙江之声--浙江频道--人民网
This page is an essay; it contains the advice and/or opinions of one or more Commons contributors.It is not a Commons policy or guideline, and editors are not obliged to follow it. Please update the page as needed, or discuss it on the talk page.
Multi-licensing means releasing content under multiple licenses. Doing so gives more freedom to users of the content, as they can choose which of the licenses best suits their needs. Multi-licensing with restrictive licenses may be desirable for compatibility with the licensing scheme of other projects; also, multi-licensing allows people who create derivative work to release that work under a restrictive license only, if they wish—that is, it gives creators of derivative works more freedom with regards to which license they may use for their work.
Multi-licensing on Commons
Many Commons users choose to dual-license their works under the GFDL and the CC BY-SA license (all versions), using the copyright tags {{GFDL}} and {{Cc-by-sa-all}}. Both licenses have a ShareAlike restriction, ensuring the work will remain free no matter how it is used or modified. Using 'all versions' of the CC BY-SA license maximises re-usability for sites which may be "stuck" with an earlier version of the CC BY-SA license.
Contributors to Wikimedia Commons can offer as many licenses for a file as they wish, as long as at least one of them meets the criteria for free licenses specified in the licensing policy. For example, files under a "non-commercial" license are OK only if they are at the same time also released under a free license that allows commercial use.
Copyright holders can release a file under additional licenses at any time, but cannot revoke licenses (Commons does not permit licenses which can be revoked - see License revocation). Commons tries to preserve mention on the file's file description page of all licenses that a file has been released under, as this can provide flexibility for re-users, and helps re-users show that they are respecting the relevant copyright.
Example
How multi-licensing under both {{Cc-by-sa-all}} (CC BY-SA) and {{Cc-by-nc-sa-2.0-dual}} (CC BY-NC-SA) can allow several images to be combined in a collage that otherwise could not be:
| Licence (image 1, from Commons) |
Licence (image 2, from another source) |
Permissible licenses for collage | Explanation |
|---|---|---|---|
| CC BY-SA | CC BY-NC-SA | No license is permissible | The collage must be published under a licence which allows commercial usage (CC BY-SA) while at the same time it must be published under a licence which forbids commercial usage (CC BY-NC-SA). The collage is necessarily a copyright violation, since it can't satisfy both licenses at once. |
| CC BY-SA CC BY-NC-SA |
CC BY-NC-SA | CC BY-NC-SA is permissible | Image 2 requires a non-commercial licence (CC BY-NC-SA) while image 1 allows both commercial and non-commercial licences. The collage creator must apply CC BY-NC-SA. |
| CC BY-SA | CC BY-SA CC BY-NC-SA |
CC BY-SA is permissible | Image 1 requires a commercial licence (CC BY-SA) while image 2 allows both commercial and non-commercial licences. The collage creator must apply CC BY-SA. |
| CC BY-SA CC BY-NC-SA |
CC BY-SA CC BY-NC-SA |
CC BY-SA or CC BY-NC-SA (or both) is permissible | Both images allow both commercial and non-commercial licences - the collage creator can choose which to apply, or apply both. |
| CC BY-SA-2.0 | CC BY-SA-3.0 | CC BY-SA-3.0 is permissible | If different versions of the same Attribution-ShareAlike license are used for different images, the newer one must be used for any collage made from them. |
| CC BY-SA-1.0 | CC BY-SA-3.0 | No license is permissible | Version 1.0 of the Attribution-ShareAlike license is not compatible with later versions. |
This shows how dual-licensing CC BY-SA + CC BY-NC-SA gives more freedom than just CC BY-SA, as well as various consequences of having different versions of CC licenses.
Wikimedia multi-licensing (2009 GFDL license migration)
See also
- Commons:Multi-license copyright tags - about how to deal with multiple licenses required for US and the source country and combine them with digitization copyright tags.
- {{Multi-license}} provides a heading to explain multi-licensing when applying multiple licenses to a file.
- Commons:License revocation - on revoking licenses