Personally, I 'work around' this copyright issue by insisting the wedding couple provide their own background song for my slideshow creation. I am merely creating a piece of visual work against a piece of copyright music. It's as good as creating a slideshow without music and then asking the couple to manually play a CD while the slideshow is run. Not sure whether this holds, and precisely why my slideshow creation service is not actively promoted as a commercial service.
As for broadcasting the slideshow during banquet or any other location, it is the client's responsibility to make sure the broadcasting (performance) rights are paid. In all cases, the hotels would have already paid an annual license to COMPASS to have permission to broadcast copyright music throughout the establishment, including banquet halls.
http://www.compass.org.sg/cIndex28.aspx
If clients want to broadcast in a location where there are no coverage in the performance rights, e.g. HDB void deck, they need to pay a license to COMPASS.