That xkcd comic needs a CC link to here like this:
Permanent link to this comic: http://xkcd.com/386/ and cc notice.
This work is licensed under a Creative Commons Attribution-NonCommercial 2.5 License.
This means that you are free to copy and reuse any of my drawings (noncommercially) as long as you tell people where they’re from.
That is, you don’t need my permission to post these pictures on your website (and hotlinking with <img> is fine); just include a link back to this page.