Suppose tht there is a website that allows users to create musical diagrams (sheet music). It is owned and operated by a person O.
Suppose the website allows users to create and share sheet music. All of the website is completely free (no registration fees and no paid features). However O has mentioned in the footer of the page that "The use of the website is not permitted for commercial purposes".
Recently O has become aware of a published book that has used diagrams made by the site's online editor, without consulting O first. Does this constitute a breach of the website terms and conditions? Is O entitled to some kind of compensation?
For info, the diagrams themselves use open source fonts for the notation of the musical symbols, and the rest is just standard sheet music. However O has a special style of presenting those diagrams on the website, which is (just) composed of a small graphical feature like a bolded line or a different coloured note symbol.
I think that because the diagram was created by the user on a free website, the user has the intellectual copyright to those diagrams. However, he created them using this website where O explicitly said that "The use of the website is not for commercial purposes". And yet the diagrams appeared in a commercially released book.
What are the legal aspects of this? What rights would O have in such a situation?