How to get YouTube Thumbnail images of a video

To show a video at website from youtube share video link, http://youtu.be/Sl9fipWZ6E0 .
we use following object code
<object width="495px" height="290px">
   <param name="movie" value="http://youtu.be/Sl9fipWZ6E0">
   </param><param name="allowFullScreen" value="true"></param>
   <param name="allowscriptaccess" value="always"></param>
   <embed src="http://youtu.be/Sl9fipWZ6E0" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="495px" height="290px">
   </embed></object>

Adode flash should be installed at your system to run the shock player.

now to show thumbnail below that video , we use VIDEO_ID - S19fipWZ6E0
http://img.youtube.com/vi/VIDEO_ID/#.jpg

where # is 0,1,2,3 .. where 2 is the default image
so our HTML code would be 
<div>
<img src="http://img.youtube.com/vi/Sl9fipWZ6E0/2.jpg">
</div>

a thumbnail image as above will display at the page