BusterSenshi
Liking YTtalk
From YouTube:
Source: http://youtubecreator.blogspot.com/2012/08/expanding-custom-thumbnails-to-more.htmlOver the next few weeks, we'll be granting access in weekly batches to partners. Partners need to have been active for 30 days and in good standing. When you get access, you should only upload images that are representative of your video, ideally featuring prominent stills from your video. Thumbnails must comply with our Community Guidelines, so abuse of this feature can result in strikes against your account and account termination.