Originally Posted by duckduckgoose

using the PHP language (with the GD graphics creation extension installed), you can create images (gif, jpeg, etc) on the fly. You can also load in existing ones and manipulate them.

So in this case, you'd load in a jpeg with a girl holding a large white sign, and then on the coordinates of the photo where the white sign was, you'd add text saying the name of the viewer's city or whatever exactly on that whitespace.

I can build one custom for you if you like - hit me up if you want. Otherwise, there are some simple examples on the web, but they aren't all the way what we're describing here.