Take a screenshot of specific application

Question

I'm running compiz under Linux. I know compiz is able to keep all workspaces running at the same time, so if I want to take a screenshot of an application, regardless of which workspace it is on, what should I do? (Any language.)

Answer 1

xwd -id x_window_id | xwdtopnm | pnmtopng > image.png

Or use the -name option to xwd.