video thumbnail

hey fellas, So i am having a hard time to figure this one out so i decided to ask for help... i created an adult tube site and im using detube wordpress theme and wp tube plugin pro to get all the content. So when i post new videos, everything works fine except the thumbnail. it wont show on...

Is there anything you can do with a video before uploading it to make YouTube give you a Thumbnail that you want? Would having the exact same frame at the very end for a few seconds do it?