4K HD Wallpaper: Wrecked Airplane
Something unusual as phone or desktop background, but because is unique this image looks really good and is free under CC0 license. Of course the photo is optimized for use in social media, web design projects, blogs, content marketing...
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)