This is simple guide on how you can use a custom wallpaper on your ps4 console.
Via PS4 Browser
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”
Via USB Drive
Create a top-level directory on your USB drive called “Images”
Visit ps4wallpapers.com on your PC/MAC and find the wallpaper you want to use, save it to the “Images” directory on your USB drive.
On your PS4 go to “Settings” > “Themes” > “Custom”, choose “Select File” and “USB Storage Device”Select the wallpaper you want to use.That’s all!