There is a pattern in which URLs to generate image thumbnails are created by Amazon, YouTube. The trick to get the images is to manipulate these URLs.
Check these detailed notes on how an Amazon URL to fetch an image is built.
As per this discussion thread, you can adapt the format of the YouTube URLs by replacing the actual VideoId in this URL to get thumbnail images of dimensions 130x97 -
http://img.youtube.com/vi/{VideoId}/1.jpg
and use this for a 320x240 image -
http://img.youtube.com/vi/{VideoId}/0.jpg
You may have to check for the licensing terms before you use them.