One of the biggest problems people have with re-using Creative Commons licensed work is understanding the way the licences can impact the way you combine or re-use the source material. When adapting CC lincensed work, you must ensure the licences are compatible with each other, and that the licence you apply to your own work is compatible with the licences of the sources you have used.
- You cannot combine material from works with licences that are not compatible.
- You cannot publish an adaptation of a CC licensed work with a licence that is not compatible with the original source material, or in a manner that contravenes the conditions of the source material's licence.
Creative Commons licences and their conditions
It will help to remember that the CC licences are giving you permission to do something in advance, so you don't have to ask. Within copyright law, only the copyright holder is allowed to make copies available and re-use their work for other projects. If you want to distribute copies of something or adapt another person's work, you have to ask for permission - and you will be given permission to do certain things with certain conditions. For example, you might be given permission to use their images, but only if it isn't for a commercial product that you're going to sell.
The CC licences give permission in advance so you don't have to ask for it, but they specify what you have permission to do:
BY (attribution): reuse, redistribute, remix for any purpose - but always acknowledge the author and respect their moral rights
NC (noncommercial): don't use this for commercial purposes
ND (no derivates): don't make any changes
SA (share alike): share this and anything made from this with the exact same conditions the author has stipulated
If you see a CC BY-NC licence, think to yourself "this person has given permission for me to reuse, redistribute and remix this work on condition that it is not made available for commercial purposes without going back and asking the author for permission".
When you see a CC BY-SA work, think to yourself "this person has given permission for me to reuse, redistribute and remix this work on condition that it is shared with the exact same licence".
Similarly, if you see a CC BY-NC-ND licence, you should think "this person has given permission for me to reuse and redistribute this work on condition that it is not altered or remixed, or made available for commercial purposes."
Any use that is beyond what the author has given advanced permission for will require going back to the copyright holder to ask for permission to use the material.
You must not make CC licensed work available to others in a way that contravenes the conditions set by the original. You cannot make a work more "open" than the copyright holder has allowed.
The copyright holder has decided how they are willing to make their work available, and you must respect their wishes
Compatibility of Creative Commons licences
Some material made available under Creative Commons licences can be used with or "remixed" with other CC licensed material, but only if the licences are compatible. You can use a Creative Commons compatibility chart (see below) to determine if the material you are using has compatible licences.
Two of the examples given above, CC BY-NC and CC BY-SA are not compatible licences. If you combined parts of those two works together, you would have to share it with either a CC BY-NC licence (which contravenes the CC BY-SA conditions of the other work, because you aren't sharing it with the same licence), or a CC BY-NC licence (which contravenes the CC-BY-NC conditions, because you are making it available for commercial use). Even though each licence allowes you to re-use and remix the material, you can't use the works together because the licences are incompatible.
The work with the CC BY-NC-ND licence is incompatible with all other licences because the ND condition means you cannot change it in any way.
Image: CC License Compatibility Chart, by Kennisland, published under a CC0 licence.
