I've just finished an upgrade and again needed to change the files to get an option I really like: On the pages with all the collections and albums a random thumb is displayed for every collection or album.
As far as I can find this is not possible to set anywhere.
What I did was this:
in "plog-functions.php"
"function plogger_get_collection_thumb()" change the line $thumb_query .= " `parent_album`='".$rv['id']."' ORDER BY 'date_submitted' DESC LIMIT 1"; into $thumb_query .= " `parent_album`='".$rv['id']."' ORDER BY RAND() DESC LIMIT 1";
"function plogger_get_album_thumb()" change the line $thumb_query .= " `parent_album`='".$rv['id']."' ORDER BY 'date_submitted' DESC LIMIT 1"; into $thumb_query .= " `parent_album`='".$rv['id']."' ORDER BY RAND() DESC LIMIT 1";
This is an easy change, but unfortunately it's a pain in the ass to think of how I did it every time I upgrade to a newer version (not often so I forget ;-) ) Maybe in the manage album/collection screen you can add the random thumb to the list with auto and all pictures?