We will be creating a website for a large clinical trial. The catch is that this trial will have study sites in many different areas of the world. We want to appeal to use user depending on their demographic. For example, when a user from one of our Thailand sites visits the website, we want them to see photos of Asian study participants (from photos we provide). Is this a possibility? It would sort of be like text translation but with photos instead.
If I'm understanding you correctly, this is possible using the standard Craft Pro "locale" stuff. In addition to making text translatable, you can make Assets translatable - in which case you can upload a different image for each translated region. The appropriate asset will be used. This assumes you target each region by having a dedicated URL prefix for each (mysite.com/thailand, mysite.com/japan etc)
I've used the Craft Geo Plugin for a project previously and it worked really well. It allowed us to serve specific content to detectable regions and areas, so that sounds like what you're after: