if user want to get the thumbnail image from a YouTube video is very easy. you can use the given link, replacing youtube id. after getting image url you should be img src tag to display image.
Thumb image:
$thumbURL = ‘http://img.youtube.com/vi/’.$youtubeVideoId.’/0.jpg’;
// Display thumbnail image
echo ‘‘;
Thumb image:
http://img.youtube.com/vi/
/1.jpg
Thumb image (different position):
http://img.youtube.com/vi/
/2.jpg
Thumb image (different position):
http://img.youtube.com/vi/
/3.jpg
Default thumb image:
http://img.youtube.com/vi/
/default.jpg
High quality large image:
http://img.youtube.com/vi/
/hqdefault.jpg
Very large (max res) image:
http://img.youtube.com/vi/
/maxresdefault.jpg