I'll keep this brief. Currently, I'm working on a website and wish to put "© 2017 [My Site]" in the footer, but a fair chunk of the content will essentially be owned by others. I don't expect to have any legal issues with this, but would like to credit them in the footer. Would I also add "© xxxx - xxxx [Company]" or something else? I don't want to be claiming that I own the companies in question.
The normal practice, which you see in copyright notices of many books, is to give a copyright notice with the primary author and date of the complete publication and then to have a series of statements about specific portions that are copyrighted by others such as "The Poem Violets Are Red, Roses Are Blue" used by permission from XYZ author, copyright XXXX. The preface to chapter 2 used by permission from XKTD author, copyright XXX. The preface to chapter 3 was published by ABC author, with copyright XXX and is now in the public domain. The preface to chapter 4 follows the diagram from Joe Smith, et al., "Big Charts Are Cool", 45 Nature 456 (2015) and is considered to be "fair use" under [statutory cite to copyright law].
A more abbreviated version might have a copyright notice and then say "no claim is made to the material appearing in quotation marks which is quoted as "fair use" for the educational and literary criticism purposes."
Of course, if you can't make a notice like one of these, you are probably violating copyright law by using a fair chunk of content owned by others.
A formal claim of fair use is not required to do so, of course, and a de facto fair use claim can be clear from context, such as citation to a source and quotation marks without a statement that the material is used by permission which is almost always a condition of a license or other permission to use someone else's copyrighted work.