Jose edit: playing with the attachment thing. Here's what I figured out: If you upload an attachment, place it inline, preview it, right click on the image to get the URL, put that URL inside img tags, you'll put the image where you want it, and there will be a redundant attachment. If you delete the attachment (from the post), the attachment remains on xkcd, the URL remains valid, and the image inside img tags remains visible and quotable, without the need for a spoilered redundancy. It's what I did here. Let me know if this did not work.