Shoutbox

There is no way to detect that because... everybody who have you on their contact list (and havng DPs shown instead of the icons) will automatically see your DP. Including anybody who has you in their hotmail contacts list, anybody who views your profile, anybody who goes to your space, skydrive, etc, etc, etc. You even don't need to be online for that, because stuff like that is stored on the servers and cached locally on your contacts' computers. Almost the same goes for the scene.

The only thing you could 'detect' in theory is when your Messenger syncronizes the DP and scene with what is stored on the server. But that doesn't say anything about who sees it at what time.