Does it have to be gray? You could just set the opacity of the image lower (to dull it). Alternatively, you could create a <div>
overlay and set that to be gray (change the alpha to get the effect).
html:
<div id="wrapper">
<img id="myImage" src="something.jpg" />
</div>
css:
#myImage {
opacity: 0.4;
filter: alpha(opacity=40); /* msie */
}
/* or */
#wrapper {
opacity: 0.4;
filter: alpha(opacity=40); /* msie */
background-color: #000;
}