Just had fun testing a phot slide show on the website. After much searching I found this article http://office.microsoft.com/en-gb/sharepoint-help/add-a-slide-show-to-a-web-page-HA104092377.aspx that shows how you use the internal team site.
The webpart is not available by defaul on the public website, but you can download it from the team site and upload it to the public website.
The webpart is: MSPictureLibrarySlideshow.webpart
Have fun
