E.g. I have a link
http://img.youtube.com/vi/aOPGepdbfpo/0.jpg
for a youtube video thumbnail:
Use it as a background image, center it and change height.
http://dabblet.com/gist/4012604
.youtubePreview { background:url('http://img.youtube.com/vi/aOPGepdbfpo/0.jpg') center no-repeat; height:204px; width:480px; }