This is because I’ve included Yahoo mRSS extension as part of my experimental Coppermine RSS/ATOM plugin.
You can see the screenshot of “My Yahoo!” here when it reacted on RSS feed that contain mRSS extension. The normal RSS/ATOM feed subscription is on the right, while the mRSS-enabled feed is in slideshow mode.
Other photo gallery that supports Yahoo mRSS is Flickr
You can get Yahoo Media RSS extension specifications here : http://search.yahoo.com/mrss/mrss