For each YouTube video, there are multiple thumbnail image URL formats that we can display/get manually. Or we can program to download thumbnail image from your uploaded video and show them in your own gallery.
Below are YouTube Thumbnail Image URL Formats include default (480×360), small(120×90), high quality (480×360) and maximum resolution.
Assume we have a YouTube video with ID: tgf8ntVVp4Q, its thumbnail image urls will be:
1. Large Default Thumbnail Image – Width:480 x Height:360
+ http://img.youtube.com/vi/tgf8ntVVp4Q/0.jpg
2. High Quality Thumbnail Image – Width:480 x Height:360
+ http://img.youtube.com/vi/tgf8ntVVp4Q/hqdefault.jpg
3. Small Image Thumbnail URLs – Width:120 x Height:90
+ http://img.youtube.com/vi/tgf8ntVVp4Q/default.jpg
+ http://img.youtube.com/vi/tgf8ntVVp4Q/1.jpg
+ http://img.youtube.com/vi/tgf8ntVVp4Q/2.jpg
+ http://img.youtube.com/vi/tgf8ntVVp4Q/3.jpg
4. Medium Quality Thumbnail Image – Width:320 x Height:180
+ http://img.youtube.com/vi/tgf8ntVVp4Q/mqdefault.jpg
5. Maximum Resolution Thumbnail Image
+ http://img.youtube.com/vi/tgf8ntVVp4Q/maxresdefault.jpg
View in another tab as it’s quite big.