How to grab a screenshot of a 4x4 screen composite display?

I'm supervising a number of headless displays, and in order for me to see, remotely, what a screen is currently displaying without actually going there and look at it, I'm using scrot to take a screenshot every once in a while. However, one of our displays is a 4x4 (that is, 16-monitor) huge display, and if I use scrot, all I get is the upper left 16th of the display - I would like to view all of it. Any ideas?