Screen Capture tool that allows me to use keyboard

There are many screen capture tools, but every tool I've tried expects from its user to click and then drag the area to capture.

Is there a tool that allows me to use the keyboard for both operations, such that I can do precise captures in a relaxed manner – without holding anything? I do not want to capture just windows, but any rectangular region.

Example of usage:

• press hotkey to enter capture mode
• move cursor (cross, loupe, whatever) around using mouse/pad and keyboard.
• when I find a good starting place (top-left corner), click or press some key to enter marking state
• now, move cursor to other corner (bottom-right) of the area I want to capture, but without holding anything! Just move cursor with the mouse or using the keyboard, as before.
• when I find a good spot, click again or press some key to finalize capturing.

There is one such tool on Windows that worked this way: FastStone Capture

For me this is an essential feature. I simply want to have precision, without holding any buttons or keys.