Every video that is uploaded on YouTube generates 4 default thumbnail images. Three of the images are sized 120×90 and the fourth is sized 480×360. The three smaller images are generated to give the owner of the video a choice of which image to display for the video.

To obtain these images you will need the unique 11 digit alphanumeric Video ID found on the YouTube video.

To find the Video ID is simple. If this is the youtube video link:

http://www.youtube.com/watch?v=ckPV4q69GbU

Then the Video ID for this url would be:

ckPV4q69GbU

You will then replace the Video_ID in the url’s below with the 11 digit alphanumeric Video ID to obtain the YouTube videos thumbnail images..

http://img.youtube.com/vi/Video_ID/1.jpg (120*90)
http://img.youtube.com/vi/Video_ID/2.jpg (120*90)
http://img.youtube.com/vi/Video_ID/3.jpg (120*90)
http://img.youtube.com/vi/Video_ID/0.jpg (480*360)