4K HD Wallpaper: The Bavarian Alps
Super 4K landscape in this 4K picture taken by Wolfgang Lonien and available from his courtesy under CC By-Sa license for use as desktop background and homescreen phone.
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)