"There're no prerequisites for fair use"

That's true IF there's a case of fair use, which very often is not the case. The extremely common scenario where you include a photo on your blog or social media post that isn't yours, is virtually never fair use.

People often behave opposite to that, but that's a matter of lax enforcement. In general, you're not allowed to use a copyrighted image without permission, regardless of whether you attribute it or not.