4K HD Wallpaper: Yellow Tulips
The 1st 4K picture from Erica's portfolio featured in gallery and available from her courtesy under CC By license. Here's optimized for fit on desktop backgrounds and homescreen phones.
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)