I never heard of this. How does it work?
Wiki Rip
Newer-generation operating systems using a graphical interface tend to copy a bitmap image of the current screen to their clipboard or comparable storage area, which can be inserted into documents as a screenshot. Some shells allow modification of the exact behavior using modifier keys such as the control key.
In Microsoft Windows, pressing print screen will capture the entire screen, while pressing the alt key in combination with print screen will capture the currently selected window. The captured image can then be pasted into an editing program such as a word processor, email, or graphics software. On keyboards that have an F Lock key, you may have to press F Lock first. Pressing print screen, with both the alt key and shift key pressed, turns on a high contrast mode for people with visual impairments.
In GNOME and KDE desktop environments, print screen behavior is similar to that of Microsoft Windows by default. However, a window will additionally pop up, prompting to save the screenshot to a file (in the PNG format by default).
Macintosh computers do not use a print screen key. Instead, the key sequence command-shift-3 provides a similar functionality, saving the image to a file on disk. To capture only a selected area of the screen, use command-shift-4 to display a cross-hair cursor which can be dragged over the required area (while the cross-hair is showing, a press of the space-bar brings up the further option to select a window to copy). Any of these key sequences save a file to the user's desktop, additionally pressing the control key will modify the behavior to copy the image to the system clipboard instead.
