You can get the users image by using a url like this:
You can get just the username and image thumbnail by appending a query string as described in the
partial responses api:
?fields=yt:username,media:thumbnail
You can get the response in json format to use easily in javascript by appending:
&alt=json-in-script&format=5
You can also specify a callback to execute when the response has loaded by appending: &callback=showImage
Your url now looks like this:
http://gdata.youtube.com/feeds/api/users/communitychannel?fields=yt:username,media:thumbnail&alt=json-in-script&format=5&callback=showImage
To use this in a page put it in a script tag like so:
<script type='text/javascript' src="your_url"/>
and the callback should look like this:
function showImage(data)
{
var name= data.entry.yt$username.$t;
var url = data.entry.media$thumbnail.url;
$(document).append("<img src='"+ url +"'/>");
}
You must make sure that the showImage callback function is defined before you load the data.
I have created a sample of loading a feed and the user images here (Make sure you change communitychannel to your own username or it won't work)
I can't see a better way of reducing your bandwidth than using the partial responses api;