When I notice that a question, answer or comment links to something relevant, but obviously made available in violation of someone's copyright (like a full book complete with scanned copyright page prohibiting distribution), should I react, and how?

Does it matter if an " I'm lucky " Google query with the work's title gets to the same URL?

Same for some image that shows without user interaction (using e.g. ![description][1]) obviously made available in violation of a copyright (like an extract of a book, when either the image itself or the context makes the violation obvious)?

Any guideline on the obviousness threshold?

Note: this is not asking how to formally report a copyright violation; in particular, I'm assuming that I am NOT authorized to make the complaint on behalf of the copyright owner, which entirely prevents me from following this procedure.

• I'm sure you've seen it, but related comment from a SE mod – Cryptographeur Feb 27 '14 at 1:30
• Just guessing, but I’m pretty sure this solves the problem – unless there’s some other link I’ve missed. (lesson learned: never, ever blindly trust the first and topmost link Google presents.) Btw.: the image-snippet is quoted and should normally be regarded to be “fair use“ as OP obviously owns the book. Also, the question includes a referring link to the publisher website which directly promotes the related book from which the quote origins. In the unlikely case the publisher thinks different, a DMCA takedown request would be appropriate… – e-sushi Feb 27 '14 at 6:37
• Treat this as plagiarism, which is against site rules. Search on the main StackExchange and you'll find the default rules on plagiarism and how to handle it: post a comment asking the author to attribute sources, and flag it for moderator attention. Moderators don't handle accusations of copyright violation, but they do handle accusations of plagiarism. (Incidentally, you can also downvote if you so choose; that's a personal choice.) – D.W. May 10 '14 at 2:36