In HTML/CSS you can do something like this:

Have two instances of the image, one with what you want it to look like regularly (name it image1) and one with how you want it to look like when you roll over it (name it image2). Then you can use this code to make the changes:

<img src="image1.png" onmouseover="this.src=image2.png';" onmouseout="this.src='image1.png';" />