Oh sure, if you want to put a link in the sig, you simply need to paste the URL of the image, and it'll automatically insert it as an image (if the URL ends with .jpg, .jpeg, .gif, or .png). If the the image DOESN'T end with that extension, then you can do it as [img]http://ImageURL/whatever/picture[/img]
As for your percentages, as I said on another thread (just a minute or two ago), the attendance percentage values are calculated at night for speed, so when DKP changes during the day, some of the numbers get thrown off a bit.
After the maintainance tomorrow, I'll start looking into making them calculated on the fly again.