How to download an image used as the background in an audio YouTube video

Youtube - Background - Images

Youtube Support

http://img.youtube.com/vi/[youtube-video-id]/mqdefault.jpg
For the highest res size use this:

http://img.youtube.com/vi/[youtube-video-id]/maxresdefault.jpg
e.g. This Video: http://www.youtube.com/watch?v=IxFfxTZA6ao

http://img.youtube.com/vi/IxFfxTZA6ao/mqdefault.jpg - 310px width
http://img.youtube.com/vi/IxFfxTZA6ao/maxresdefault.jpg - 3000px width

Youtube Background