An image of paleolithic cave art in the Altamira cave is used in the app, with changes as detailed below. This image was originally published on Wikimedia Commons by Yvon Fruneau, and is available under this URL: https://commons.wikimedia.org/wiki/File:Cave_of_Altamira_and_Paleolithic_Cave_Art_of_Northern_Spain-110113.jpg

The original image is licensed under the Creative Commons Attribution-ShareAlike 3.0 IGO license.

For use in the app, the original image was mirrored, rotated and cropped. Additionally, two different color filters were applied to the image. The resulting image files can be found here, they are licensed under the same license as above.