The CD cover art is usually in a format that can be opened by the applications developed to create covert art for storage mediums. If you have the software, load the covert art and then right click the image and save it to another place, then you can use an image viewer with conversion features to transform it to JPG. XnView will do just fine.
Secondly, if the software doesn't offer the possibility to save the image, use a screen capture tool to save it. For this procedure you can use Lightshot.