These overlays (sometimes known as bezels) display art on top of the game you're playing. To use them, you need a PC or Raspberry Pi (or other compatible system) running some version of MAME and the associated game software, as well as a widescreen (16x9) monitor mounted vertically. To display the overlay while playing a game, download the artwork file for that game overlay (it must have the same filename as the game), place it in the Artwork folder within your MAME directory and launch the game. (For instance, the software for the game Magic Sword is called msword.zip, so it requires a file in the Artwork directory also called msword.zip.)
All overlays are 4K resolution (2160 x 3840), and listed dimensions are for the game screen, relative to a 4K vertical monitor. The actual game screen size will depend on the resolution of your monitor.
Most of the overlays include multiple presets that let you choose the size of the game screen, access a "dark" version designed to look more like a dark arcade, and sometimes other options. To choose a preset, press Tab while running the game to bring up the MAME menu, select Video Options, and select a preset from the list.
Some overlays include Curved presets designed with a curved screen port, to better simulate the look of a CRT monitor. These presets work best if you are using a geometry shader that adds a curved look to the game screen. For an optimal experience, you may need to adjust your shaders to match the curvature of the screen shape in the overlay. If you are not using a geometry shader, you are using a shader that adds a curved bezel, or if you prefer a rectangular screen port, choose a Straight preset where applicable.
Fully titled Ketsui: Kizuna Jigoku Tachi (“Determination: Cutting the Bonds of Hell”), Ketsui is a bullet hell shoot-em-up released by Cave during the genre's early-2000s renaissance, and remains a favorite for its punishing difficulty and unique scoring system. Though less well-known than popular Cave shooters such as Dodonpachi and Deathsmiles, Ketsui features the same type of frenetic action you expect from a Cave game, but destroyed enemies here drop chips that increase in value depending on your distance from the enemy and connect into chains if you can maintain your pace. The mechanic creates a scoring multiplier metagame that raises the intensity, while Ketsui is simultaneously less unforgiving in some areas than similar Cave games.