Rider, After you sign up you just need to delete your cookies (I find deleting them easier than editing), sign in on e-hentai and then go to exhentai. If you've visited before without an account, the sad panda will stay until you delete the cookies and sign in.
But if you don't want the hassle, Zelinkokitsune's got the right idea.
Because it's a scan, there is no web source for this specific version of the image. Sources are per individual image, so the source of the parent image doesn't apply to this one.