apparently, byzanz allows one to record a specified portion of the screen as well. check out these commands:
byzanz-record [options] filename.gif
Options
Application Options:
-d, --duration=SECS
Duration of animation (default: 10 seconds)
--delay=SECS
Delay before start (default: 1 second)
-l, --loop
Let the animation loop
-c, --cursor
Record mouse cursor
-x, --x=PIXEL
X coordinate of rectangle to record
-y, --y=PIXEL
Y coordinate of rectangle to record
-w, --width=PIXEL
Width of recording rectangle
-h, --height=PIXEL
Height of recording rectangle
-v, --verbose
Be verbose
--display=DISPLAY
X display to use
Help Options:
-?, --help
Show help options
--help-gtk
Show GTK+ Options
--help-all
Show all help options