Check http://atvdigiframe.blogspot.com/
"This specially designed software allows you to use AppleTV as a true digital picture frame without any limitations ! Set the display duration for your photos anywhere from several seconds to days !
A standard AppleTV device is limited to a maximum delay of 20 seconds between two photos in the slideshow mode. We overcame this problem and allow you to conveniently set up your own delay between photos."
"This specially designed software allows you to use AppleTV as a true digital picture frame without any limitations ! Set the display duration for your photos anywhere from several seconds to days !
A standard AppleTV device is limited to a maximum delay of 20 seconds between two photos in the slideshow mode. We overcame this problem and allow you to conveniently set up your own delay between photos."