A wedding slideshow, often prepared by friends of the bride and groom and played at the rehearsal dinner, can be a really cute way to share the story of a relationship through photos for the guests. It's a little egotistical for the bride and groom to put it together themselves so often a best man or maid of honor or sibling of the couple will take on the task of collecting photos of the bride and groom as babies, in high school, in college and throughout their relationship and compiling it to music.
A word of advice though, not everyone likes surprises! Especially surprises involving nude baby photos or drunk college photos shown to all their loved ones.
While it might seem fun for you to poke a little fun at the bride and groom an ill-timed surprise at what can be a stressful and emotional time is not the best way to kick off the weekend. I'm just saying, double check with the bride and groom that they're OK with you putting together something special for them as a surprise before you spring it on them.
I'll never forget a wedding I planned a few years ago where the bridesmaids decided to surprise the bride (unbeknownst to their planner) with live karoke. Apparently (as they told the audience) she was too embarrassed to get up and sing it on their bachelorette weekend and said she regretted it the next morning so they wanted to give her a chance to make up for it (AT HER WEDDING!?). They dragged her on stage with a microphone and told the DJ to play Tina Turner. I've never felt more helpless in my life and career as there wasn't much I could do once that train wreck got going. Thankfully the bride held it together through the song but you could just tell she wouldn't be speaking to the ringleader for a few months after that.
So just know your audience. Personally I love surprises and if I were the bride to be, I'd be very happy with a slideshow set to the tune of this song: