Choosing a wallpaper that actually looks good requires understanding your monitor's specifications and what images work well at those specifications. Most wallpaper problems are resolution or aspect ratio mismatches rather than image quality issues.
Resolution basics: wallpaper should be at least as large as your display resolution. On a 4K display (3840×2160), a 1080p wallpaper will appear soft when zoomed to fill the screen. Always download at the highest available resolution and scale down — never scale up.
Aspect ratio is the more commonly misunderstood issue. Standard widescreen monitors are 16:9 (1920×1080, 2560×1440, 3840×2160). Ultrawide monitors are 21:9 (2560×1080, 3440×1440). Apple MacBooks use 16:10 (2560×1600, 3456×2234). A 16:9 wallpaper on a 16:10 display will either be cropped or show black bars depending on the scaling setting.
OLED displays have specific considerations. Pure black pixels (RGB 0,0,0) on OLED panels turn off completely, creating true black. Wallpapers with deep dark backgrounds look dramatically better on OLED than on LCD because the contrast ratio is essentially infinite. The same wallpaper that looks flat on LCD can look stunning on OLED.
Multi-monitor setups require either one panoramic image that spans all monitors, or matched wallpapers that feel cohesive separately. Most operating systems support per-monitor wallpapers; the easiest approach is a cohesive color palette across images rather than one panoramic crop.
For Apple Silicon Macs with ProMotion (120Hz) displays: high-detail wallpapers that would appear busy on a 60Hz display can be stunning at 120Hz because the eye's ability to process fine detail increases with refresh rate.