Are you looking for a way of doing this with Vimeo? Have a look over there:http://coderwall.com/p/fdrdmg
Let's say you need an image preview of a YouTube video.
If, for instance, this is your video: http://www.youtube.com/watch?v=LFbhGEiFWk4, simply type http://img.youtube.com/vi/LFbhGEiFWk4/0.jpg in your address bar, and voilà!
The gritty details
YouTube automatically generates (at least) three thumbnails and one image preview for every uploaded video, and you can easily get to them once you know how.
First of all, take a look at the URL of the video you're interested in. They all are formated like this:
Where VIDEOID is a string of letters and numbers uniquely identifying it. You may have an ampersand (&) and some arguments after that ID, but you can safely ignore them.
Take note of (or copy) that VIDEOID string.
In order to get the YouTube generated thumbnails, you'll simply use the following address:
Replace VIDEOID with the aforementioned string, by typing it or pasting it in. Don't it ENTER yet!
You first need to decide which thumbnail you want. Try them out for size by replacing the hash (#) with a number, like this:
Will give you the default large preview image (480x360). For our example, this gives us:
Will give us the first small thumbnail (120x90):
Will give us the second small thumbnail (120x90) or the thumbnail chosen by the uploader for that video (this is the default thumbnail for YouTube):
Will bring back the third small thumbnail (120x90):
Bringing it further
By knowing this logic behind YouTube's thumbnails and preview images, writing up a simple script able to show the images for any given video becomes rather trivial and will be left, as the saying goes, as an exercise for the reader.
Of course, Google makes it even easier by providing us with a YouTube API: http://developers.google.com/youtube/2.0/developers_guide_protocol - what you're looking for specifically is the information about the media:thumbnail tag: http://developers.google.com/youtube/2.0/reference#youtube_data_api_tag_media:thumbnail
N.B.: I know this is nothing new or heart-shattering, but I always seem to forget which URL gives which image. So, here it is for our reference, and if this can also help one of you, then all the better!