4K HD Wallpaper: Challenger Tank
From Steve's courtesy the 4K picture can be downloaded under CC By license and use as desktop backgrounds and homescreen phones if you like it.
Widescreen Desktop / Macbook: 2560x1600 (fits on: 1920x1200, 1440x900, 1280x800)
High Definition HD 1080p: 1920x1080 (fits on: 1600x900, 1366x768, 1280x720)
Samsung Galaxy Tab & iPad: 2048x1536 (compatible with almost all tablets)
HTC, Samsung Galaxy & iPhone: 1080x1920 (compatible with many smartphones)