问题
if one desktop isn't the current desktop，so，windows will not draw it .then capture the screen by DC was not work.
help me!!!
回答1:
The best you can do is to use the technique described in this article:
http://www.fengyuan.com/article/wmprint.html
Basically, you have to fool the applications on the other desktop to redraw their windows into a DC of your choice. I did this once - it can be made to work, but it's by no means trivial.
There are many drawbacks - e.g. don't expect to be able to show a nice Aero style composited desktop.
来源：https://stackoverflow.com/questions/5643637/how-to-capture-screen-from-another-desktopcreatedesktop