From Sega Retro
This template sets the maximum width of a screenshot to 320 pixels, and corrects its aspect ratio.
This is how the game appears on an actual Sega Game Gear. The original image taken from an emulator is below:
"width" also takes into account the adjusted aspect ratio, so the image appears 120 pixels wide even if the source image is not.
In addition, this template corrects heights:->