here's an easy working setup - depending upon how your storing your photos download to a laptop (preloaded with adobe bridge and video out) with a portable HD attached. Once your have a folder with the images on the laptop's HD make a copy to the portable HD and unmount the portable HD and put in a safe/secure place.
Load bridge and use it's slideshow feature - the DJ can continue playing his music and you can control the slideshow right from the laptop.
update - I see there are now external hard drives with media readers built in and video out connections. some are just the enclosurers and you add the HD and some are complete units - anyway just load copies of your images and let it play ( I even saw one that supports playback or RAW files).
I'll have to get the model numbers