Image class isn't supported by MSIE 3.x and NN 2.x. A skin is a set of graphics used by an application to create it's appearance.
Skins allow users to create their own look and feel to an application.
A lot of the time people customize their applications like this purely for cosmetic purposes. Some applications however allow you to change their functionality or productivity features as well. Not all applications support skins, but our Cool Desk , ZVolume Pro and SClock Plus do. We encourage you to make skins. Create one and send it to us and you will be included in our weekly skin drawing contest.