4K HD Wallpaper: Police Car
At full 4K the original image isn't really sharp, but at 1080p looks perfect or for mobile devices. The photography was taken by Matt Popovich near the White House, Washington, US and from his courtesy can be downloaded completely free under CC0 license for use in non-commercial and commercial (templates, blogs, apps...) projects.
Widescreen Desktop / Macbook (Retina): 2880x1800 (fits on: 2560x1600, 1920x1200, 1440x900)
High Definition HD 1080p: 1920x1080 (fits on: 1600x900, 1366x768, 1280x720)
Samsung Galaxy Tab & iPad: 2048x2048 (compatible with many tablets)
HTC, Samsung Galaxy & iPhone: 1080x1920 (compatible with many phones)