
A screenshot (also known as screen capture or screen grab) is a digital image that shows the contents of a computer display. A screenshot is created by the operating system or software running on the device powering the display.
Additionally, screenshots can be captured by an external camera, using photography to capture contents on the screen.
On Windows, pressing PrtScr captures a screenshot of the entire desktop, while Alt+PrtScr captures only the active window. Captured screenshots do not include the mouse pointer. Windows places these captured screenshots in the clipboard, meaning that an additional program needs to retrieve them from the clipboard. Starting with Windows 8, however, ⊞ Win+PrtScr or ⊞ Win+Volume up instantly saves a screenshot to the “Screenshots” folder in “Pictures” library. All screenshots are saved as PNG files. Note: On some notebooks you have to hold Fn and then press PrtScr instead.
Lightshot gives more power to your screenshot with additional features like:

So how to install?
The process is very very simple, just go to here download the exe and follow the instructions. When ready press the print screen button on you keyboard and check out how many new options you have!
Digital techniques
The first screenshots were created with the first interactive computers around 1960. Through the 1980s, computer operating systems did not universally have built-in functionality for capturing screenshots. Sometimes text-only screens could be dumped to a text file, but the result would only capture the content of the screen, not the appearance, nor were graphics screens preservable this way. Some systems had a BSAVE command that could be used to capture the area of memory where screen data was stored, but this required access to a BASIC prompt. Systems with composite video output could be connected to a VCR, and entire screencasts preserved this way.
Most screenshots are raster images, but some vector-based GUI environments like Cairo are capable of generating vector screenshots.
Photographic techniques
Screenshot kits were available for standard (film) cameras that included a long antireflective hood to attach between the screen and camera lens, as well as a closeup lens for the camera. Polaroid film was popular for capturing screenshots, because of the instant results and close-focusing capability of Polaroid cameras. In 1988, Polaroid introduced Spectra film with a 9.2 × 7.3 image size more suited to the 4:3 aspect ratio of CRT screens.