A tank is an armoured fighting vehicle designed for front-line combat, with heavy firepower, strong armour, tracks and a powerful engine providing good battlefield maneuverability. The first tanks were designed to overcome the deadlock of trench warfare in the 1910s; they are a mainstay of modern ground forces and a key part of combined arms combat. Modern tanks are versatile mobile land weapon system platforms, mounting a large-calibre cannon in a rotating gun turret, supplemented by mounted machine guns or other weapons. They combine this with heavy vehicle armour which provides protection for the crew, the vehicle's weapons, and its propulsion systems, and operational mobility, due to its use of tracks rather than wheels, which allows the tank to move over rugged terrain and adverse conditions such as mud, and be positioned on the battlefield in advantageous locations.
Chroma key compositing, or chroma keying, is a special effects / post-production technique for compositing (layering) two images or video streams together based on color hues (chroma range). The technique has been used heavily in many fields to remove a background from the subject of a photo or video – particularly the newscasting, motion picture and videogame industries. A color range in the foreground footage is made transparent, allowing separately filmed background footage or a static image to be inserted into the scene. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as color keying, colour-separation overlay (CSO; primarily by the BBC), or by various terms for specific color-related variants such as green screen, and blue screen – chroma keying can be done with backgrounds of any color that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from most human skin colors. No part of the subject being filmed or photographed may duplicate the color used as the backing.