Is it too much to ask to give credit where credit is due? Or to ask the artist if it’s okay before reposting their works? If you can find where those cute pictures of Locke and Asami came from, I’m pretty sure contacting the artist isn’t that much more work. And if you don’t get permission to, too bad, it isn’t your artwork anyway! If you can’t get an okay from the artist, don’t do it.