After uploading a video to youtube it randomly generates three preview images from which you can choose. Is there a way to select a specific image from the video instead?
You have to be a partner if you want the option of choosing what custom thumbnail represents the videos you upload.
This was brought up in the Partner Forum of YouTube in Custom Thumbnail update:
As many of you may know, the custom thumbnail program has been running for some time now, allowing our partner community to select custom images for their videos.
And is mentioned also in Flagging Videos > Spam of Content Reporting and Removals
Misleading thumbnails refer to users who chose a thumbnail that is not representative of the actual video content in order to gain views. Only those in the partner programme are allowed to choose their own thumbnails.