Connected Photo Frame Display
Source: Martha Stewart Living, February 2011
Just connect frames with hardware called mending plates. Try monochromatic frames and black-and-white shots for a unified look, or an eclectic mix to liven things up.
2-inch mending plates (available at hardware stores)
First, lay out frames on the floor to find the arrangement you like. Then lay out frames, face down, in the pattern you choose.
Drill pilot holes for screws, then use mending plates to connect the frames in 2 places.