So, I guess there are so many screen capture software.
If you are using the shortcut Alt+PrtScr it will take a screenshot of the current window.
The shortcut will work on Windows 7 as well as Windows 8.
The other way to capture a screenshot is to use the software that comes with Windows:
Start Menu > Programs > Accessories > Snipping Tool
In Windows 8 you should use "Snip & Sketch"
I'm not sure what you're trying to achieve, but you could write a small C program that shows the image.
It would be easier to capture the screen on Windows using Ctrl+Alt+PrtScr. You can read the MSDN for more information.
The problem is that messages are not displayed correctly. For instance: