I've written an app that updates the users wallpaper periodically. A common feature request is to also be able to update the lockscreen image as well. I was unaware that there even was such a thing as a lockscreen wallpaper, as vanilla Android just displays the same image as you have set on your homescreen, but apparantly HTC's Sense has this feature.
I can't seem to find any documentation for the extras in Sense. Ideally I'd like to be able to set it programmatically, in a similar way to using the built-in WallpaperManager and setStream. Failing that, a list of the intents that Sense responds to might be useful.