Youtube does it in flash.
You can do something similar over an image with Div tags and css
<style>
#divImage {
position:relative;
}
#divTranslucent {
position:absolute;
bottom:0px; //position from the bottom of the image div you can also use right, left, and top
height:50px; //height
background:#fff;
filter: alpha(opacity=55); //this line make its 55% transparent in IE
-moz-opacity: .55; //this line make its 55% transparent in Firefox
}
</style>
<div id="divImage">
<img src="../whatever.jpg">
<div id="divTranslucent ">Translucent Text</div>
</div>
Hope this gives you a start.