I found the layer blend was the most useful effect I used. Especially when removing whites to reveal the blacks to see the other images.

The emphasis in the first image (there are two because the backgrounds make a different effect for each) is the child reaching up for the sky. I made it stand out by having a light blue outline the edge of the arm, blue radiate off of him and have a posterized layer of the boy overlaying the original. In the second image the emphasis is the "Where's the rain?" image. It stands out because it is the whitest section on the piece being on top of a black brazil, it is different than all the other shapes on the work and it is the least altered.