You might come across videos on YouTube which have blank or terribly looking thumbnail image. Usually, when a video is uploaded, YouTube automatically picks the center frame and sets it as a thumbnail image. Users have no really control over these thumbnail images, except for some smart tricks to get their desired thumbnail image, but most of us don’t have the time or patience to practice those tricks.
YouTube realized this problem, and they’ve made it possible for users to pick one out of three thumbnail images. YouTube captures three thumbnail images at x/4, x/2 and 3x/4 seconds and video owners can choose any one of these thumbnail images by clicking on “Edit Video Info” button next to their video on My Videos page.