Highlight image hover effect is a Scripts software developed by Dynamic Drive. After our trial and test, the software is proved to be official, secure and free. Here is the official description for Highlight image hover effect:

The first example changes the opacity of any image link when the mouse moves over it using the "hover:" Pseudo class of CSS. Note the two different properties used to specify opacity in CSS below. In IE 5.5+, the "filter" property is used (range: 0-100), and in Firefox, "-moz-opacity" (range: 0-1). Both properties are proprietary, and not formally endorsed by the W3C.