I am self-publishing my dissertation and want to use a picture of a painting, modified to fit the cover and with titles and author name on it.
The painter is dead for over a hundred years and a file of the painting can be found in Wikimedia Commons licenced under the GNU Free Document Licence.
I am unsure about the implications. If I use this file in a modified version in a commercial product, I have to include a printout of the GFDL in my book as well as ensure that the original file can be downloaded. Is this correct?
I also have to release the modified version under GFDL. Does this only apply to the book cover then? That would be fine. But I do not want to release the whole book under GFDL.
What else do I have to pay attention to?