For this effect I used Dan Ebberts falling leaf expression along with suggestions posted on a C Cow thread. Tweaked it a bit.
Keyframed the Null's sliders for Z Rotation & Y Rotation max tilt. Since all of the photos are controlled by one null I adjusted each photo's Z Orientation & X Rotation for the background photos and for the front photos the Z Orientation only.
The advantage of having all photos to one null is that you can change the parameters globally. The downside is that they will be too uniform. This project was for an intro to a slideshow segment (I swapped out my personal photos for this video) and I only had about a dozen photos. If a project had many photos and showing many at one time, you could divide the photos up between 2 or 3 nulls for variety in flow.
Music: Unwind by Ron, Muvipix composer & Admin. Thanks Ron!