Making Multiple Images Work Together

How do you make a presentation's imagery consistent when pulling that imagery from multiple sources?

An old trick is to apply a consistent effect to all the imagery like turning it black and white or creating duotones.

But in a presentation we created last week, one of my designers was even more careful when composing collages. She made sure that the image subjects physically worked together, and I loved how they turned out: The orbital rings overlayed on the woman's head...the Great Wall melting into the UN dais.

Awesome job, Carinda! Here are a couple of the slides from that presentation.