It's about an app that was created in a student project (in Germany) and will be soon released in the Google Play Store and also published on GitHub as OSS under the MIT license. The app features illustrations that some of the students created themselves.
We are now unsure about the legal situation with these illustrations: using just the MIT license, is it allowed to use/modify/distribute only the illustrations of the OSS without touching the program code at all? Is it possible or necessary to add additional copyright notes to them, in the app itself or somewhere inside the GitHub project (e.g. Creative Commons with author attribution) or are they automatically under the MIT license as well?
Thank you in advance if anyone is familiar with this topic :-)