Screen capture on locked workstation yields a blank image?

[aagnone3]

I am looking for a way to take screenshots on a workstation while it was locked. I have a script that will be performing several actions, and want to be able to take captures of the screen at various points throughout the script. However, even when using _screencapture_capturewnd and providing specific handles to windows, the capture yields a blank image. To verify this, I made a script that takes a screenshot, locks the computer, and then takes another. The result is a successful image before the lock and a blank image after. Does anyone have a solution to this?

[BrewManNH]

You can't capture the screen of a locked computer.

[water]

Why do you want to take a screenshot.

Have the script write to a log file so you can monitor the progress this way.

[aagnone3]

I already have a log file, but am automating other software which has visual elements I would like to track. 

[water]

Which application do you try to automate? I'm sure AutoIt has functions (Control* etc.) to let you do what you want without taking screenshots.

[aagnone3]

It is a company-developed software. I am achieve everything I want to, but simply want the screenshots as extra verification and a quick reference to look back on different states of the script's process.