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 Site Name > Appearance > Customize.
The responsive skins use a banner widget that can be added to the home page of your site. This option can be found by navigating to Site Name > Appearance > Widgets. You can upload images to a number of slides within a rotating banner and control the behavior of the banner via the options within the widget.
Please see this article for instructions on updating your banner images via the widgets area: