Created a "mat" by adding a layer of white atop the three combined images. Lowered the opacity on the white top layer so that I could make my cut outs. Then used the inner bevel and drop shadow functions to give the mat a 3 dimensional look. Added another layer for the second "mat" and again used drop shadows and inner bevel. Added a border and then ran Super Blade Pro to give it a frame like look. Then converted all to black and white since the greens in the various photos were too different to really look nice together in my opinion.