See sig... it downloads the small rotating thumbs from each site now. You can view a list of how many thumbnails each site stores at
http://www.tubescraperpro.com/status.php
If the small thumbnails aren't the size you're looking for, then as Konrad said, you're going to need to download the full FLV file. Assuming you can ffmpeg installed on your server, this can all be automated as well though. Scraper downloads the FLV, makes thumbnails is desired size, does whatever you want with them, then deletes the FLV.
Contact me if you have any questions.
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