It is somewhat redundant with software that can capture from the screen into virtual webcam devices that are then trivial to publish with ros, though they would lack the ability to be controlled through ros parameters.
https://code.google.com/p/webcamstudio worked well for virtual webcams but I haven't tried it in a couple of years.
It probably only works correctly with a X windows setup similar to what I have on Ubuntu 12.04, there is no attempt to convert the image out of XGetImage for special cases.
If the screen spans multiple monitors and the roi crosses the window boundary and is partially in and out of the display area it might crash, I haven't tried that. I'll add publishing of the max width and height next.
It's written for catkin and Hydro.
Any feedback and inclusion into the package list would be welcome-
Lucas Walter