• Take a picture of a window
• Take a picture of a specifed window with a timer
• Take a picture of entire screen
• Take a picture of entire screen with a timer
• Save a serie of pictures without name file confict
• Post procession (Zoom, Grop area)
• Copy to clipboard for easy share screenshoot

That require to work with low level XLib like it exemple:
https://www.initbrain.fr/code/2015/screenshot-tool/