Im a big fan of Screenshot Helper Addon and I wish, I could have that blur effect only and all time while playing. I try hard, but I dont know nothing about scripting, and all I found in the code was this:
Replace x and y with the x axis and y axis coordinate values on your screen.
if you run a resolution like 1920x1200 x can be a value between 0 and 1920 and y between 0 and 1200.