Another trick is to take an image snapshot of a YouTube video and call it keyword-video.png since some people search on Google Images for videos. Then on your site, link to the video in a new window so your site stays in the browser.
Also, the alt tag is vitally important.
For a good example search on (in G image search): susan boyle video
The top results are for a .org.uk site that gets most traffic from this search method and made $400 in the first month as I recall.
I'm not sure if making the image larger in this case would work since videos have standard sizes.
m42 (9 October, 2010)