Help with music background art

I am fairly new to XBMC and so far love it as a replacement for WMC. I have a few questions as to how an clean up/add/delete some images within Music. I am confused as to the nomenclature about all the images that are available. There is mention of fanart, album art, artwork (downloader), etc. What I need help with is the artwork that is downloaded as a background for a group or artist and which changes every 30 seconds or so (if more than one image is available). Not sure what XBMC calls this (background fanart??). My problem is some of the images that were automatically downloaded when I first set up XBMC is horrible or not of the artist that it’s supposed to be. Some of the pictures only show the tops of the heads of people, some are cut off from the sides, or I get a picture of the wrong artist or group.

My questions are:
*Where does XBMC store these background images? I take it they are separated in folders by artist.
*Can I delete the ones I don’t want?
*How can I add new images/photos to show up for a group or artist in the background, either manually or through an add-on?

Thanks in advance for any help you can give me.