How to set thumbnails for videos

We've realised that there are a lot of videos without thumbnails. Unfortunately, thumbnails cannot be extracted automatically. Since videos without thumbnails are boring, we decided to write a small tutorial on how to do it: http://wua.la/en/howto/start07/

You can set thumbnails for your own videos or for videos in the public area that do not have a thumbnail yet. However, the thumbnail can only be removed by the owner of the file. In order to remove the thumbnail you need to double click the thumbnail and press "remove image".