The CSS3 property for transparency is opacity.
img {
opacity: 0.4;
filter: alpha(opacity=40); /* For IE8 and earlier */
}
Image Transparency - Hover Effect
<!DOCTYPE html>
<html>
<head>
<style>
img {
opacity: 0.4;
filter: alpha(opacity=40); /* For IE8 and earlier */
}
img:hover {
opacity: 1.0;
filter: alpha(opacity=100); /* For IE8 and earlier */
}
</style>
</head>
<body>
<h1>Image Transparency</h1>
<img src="klematis.jpg" width="150" height="113" alt="klematis">
<img src="klematis2.jpg" width="150" height="113" alt="klematis">
<p><b>Note:</b> In IE, a !DOCTYPE must be added for the :hover selector to work on other elements than the a element.</p>
</body>
</html>