To add a hover image to and image, add this code:
onmouseover="this.src='/media/hover-image.png';" onmouseout="this.src='/media/default-image.png';"
Inside the img tag:
<img alt="" src="/media/default-image.png" />
So that it looks like this:
<img src="/media/default-image.png" onmouseover="this.src='/media/hover-image.png';" onmouseout="this.src='/media/default-image.png';"/>
Change the onmouseover source to the image you want to show on hover and onmouseout source to the default image.
