gnome-screenshot copy to clipboard shortcut

There are a set of keyboard shortcuts in Ubuntu specifically for screenshots.

Go to System Settings > Keyboard > Shortcuts > Screenshots. In my case it is Ctrl+Shift+Print_Screen

I found out the solution. First, open the shortcut dialog window and press add to add a new shortcut. Then paste this code:

gnome-screenshot -a -c

For other useful gnome-screenshot command, from the terminal: gnome-screenshot --help

For Gnome, copying portion of the screen to clipboard is Ctrl+Shift+PrtScrn.