This is simple guide on how you can use a custom wallpaper on your ps4 console.
Visit ps4wallpapers.com in the PS4 browser. Browse in fullscreen mode (Square button on dualshock)
Find the wallpaper you want and click the download button
Take screenshot with Share button. (Remember to hide mouse pointer)
Open “Capture Gallery” app, go into “Other” folder then press options button on your desired wallpaper and “Set as background”