But in all seriousness, it’s really not that difficult to reblog something. There are very easy ways to find the original author of an image or post as well via google.
While I can understand wanting to post something and not knowing who original created the content, the fact of the matter is just because you find an image does not give you equal ownership to it as the person who created it. That’s not how artwork works. You don’t post something online and then whoever wants to repost it without credit is allowed to. If you can’t find credits, that’s fine. If someone asks you to credit and you refuse to on the basis of “equal ownership over the internet” then you’re just being an ass.