You can add sound effects to fit with the situations of the photos that are playing. Note sound Effects is only for photos. You can combine videos and photos together with music. I have a full sound effects library to pick the right sound for your photos.
You can use these transitions in-between the photos.
You can use these backgrounds for the start of the slide show or the end.
You can use this as an introduction to the slide show, title to describe the situation, and or giving the names of people in the photo.
You can pick a sound to fit what you see in the photo that is showing.