Deepin Screenshot tool is one great tool for grabing the area you want.
You can install that in the following way:
1.Download the source code (in Python)
If you use Debian devirants as your main system, you can download the .deb package. Double click to install it.
2. Install dependency - Python-xlib
sudo apt-get install python-xlib
3.Grab the screen
Ctrl+PrintScreen:Grab screen delayed
you can draw arrows and input characters.