Zedge offers a massive library of user-uploaded content with a specific category for robot backgrounds.
For reliable downloads without low-resolution issues, these sites are highly recommended: 1920x1080 Robot Wallpapers | Best Wallpapers
WallpaperSafari and WallpaperCave are excellent for curated collections of "best" and trending images. Zedge offers a massive library of user-uploaded content
WallpapersWide provides a helpful rating system and allows you to select the exact resolution for a perfect fit. 1920x1080 Robot Wallpapers | Best Wallpapers