The Moriarty skin features a banner that rotates through images. Here is an example:
If you would like to have this feature in a site that uses one of our standard skins other than the Moriarty skin, then you could create a flash file and upload it to the home page banner area in Sites > Skins > Customize Skins.
The responsive skins use a banner widget found in Sites > [site name] > Widgets. You can upload images to a rotating banner and control the behavior of the banner via the banner widget. Please see this article for instructions on updating your banner images via the widgets area: