I participated in last week's core dev chat, and in my feedback for feature plugin Press This, I raised a question with the team about copyright infringement possibilities. I asked, because when testing, I used a full-size image from Politico for the post I did, which was prompted by Press This.
They linked me to the Github issue where Daniel Bachhuber brought up the same thing. Anyway, it appears everybody — including the new “WP and Legal Stuff” blog, who I sent the issue to — agree that WordPress itself is not liable. But individuals still can be.
I don't know. I guess I wish we made it harder in core to violate image copyright. It worries me a bit that I can just hijack someone else's photo like I did, and that WordPress made it super easy for me. I think this is likely a non-issue for Press This, but it is an interesting discussion and I wonder if we should take a different role than, “Not my problem what users do.”