Ok, try using import. Read the man page, you can specify how/what you want to capture. Either point and click with mouse to do one window, do a click and drag to capture a section of the screen, or collect the whole screen with something like import -window root root.jpg.
Here's a way to capture the whole screen and to allow you time to get your xterm out of the way:
sleep 5; import -window root root.jpg
And you could know when the 5 seconds is up by playing a sound:
sleep 5; import -window root root.jpg; play done.wav
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xwd - X Windows Dump
Maybe use:
use "xprop" to get window ID's
"xlsclients" - to get names
Use xview to view the resulting file
Use xprop to get WM_NAME or WM_NAME(STRING).
Use xprop to get WM_CLIENT_LEADER(WINDOW): Window Id #