Each YouTube video has 4 generated images. They are predictably formatted as follows:
[code language=”html” smarttabs=”true” tabsize=”4″]
https://img.youtube.com/vi/<insert-youtube-video-id-here>/0.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/1.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/2.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/3.jpg
[/code]
The first one in the list is a full size image and others are thumbnail images. The default thumbnail image (ie. one of 1.jpg, 2.jpg, 3.jpg) is:
[code language=”html” smarttabs=”true” tabsize=”4″]
https://img.youtube.com/vi/<insert-youtube-video-id-here>/default.jpg
[/code]
For the high quality version of the thumbnail use a url similar to this:
[code language=”html” smarttabs=”true” tabsize=”4″]
https://img.youtube.com/vi/<insert-youtube-video-id-here>hqdefault.jpg
[/code]
There is also a medium quality version of the thumbnail, using a url similar to the HQ:
[code language=”html” smarttabs=”true” tabsize=”4″]
https://img.youtube.com/vi/<insert-youtube-video-id-here>/mqdefault.jpg
[/code]
For the standard definition version of the thumbnail, use a url similar to this:
[code language=”html” smarttabs=”true” tabsize=”4″]
https://img.youtube.com/vi/<insert-youtube-video-id-here>/sddefault.jpg
[/code]
For the maximum resolution version of the thumbnail use a url similar to this:
[code language=”html”]
https://img.youtube.com/vi/<insert-youtube-video-id-here>/maxresdefault.jpg
[/code]
All of the above urls are available over http too. Additionally, the slightly shorter hostname i3.ytimg.com works in place of img.youtube.com in the example urls above.
Alternatively, you can use the YouTube Data API (v3) to get thumbnail images.
