A bunch of wallpapers has been released on the official Metal Gear Solid Snake Eater Pachislot website, each available in 12 different sizes, 6 for desktop PC and 6 for mobile platforms.
Below are the largest PC resolution (3840 x 2160) and the most common smartphone size (1080 x 1920), for the other resolutions head to the official website
[no longer up].
The website has also updated its art segment, in which the characters are introduced.
Source: KPE Official Website [no longer up], PachiSlot Official Twitter