4K HD Wallpaper: It's okay to eat a whole pizza by yourself
A funny 4K image made by Glauco Barbosa Moreira can be downloaded from here free for personal use as desktop background and homescreen phone.
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 almost all tablets)
HTC, Samsung Galaxy & iPhone: 1080x1920 (compatible with many smartphones)