Wallpaper laptop?

I had a background image from the Internet on a laptop (Mac). However, whenever I turn off the laptop, the picture is removed and one from Apple itself sets itself. Does anyone know why this is?

The picture is probably subject to a "copyright" from the Internet and will therefore be removed automatically. Just a thought…

Funny, I often had a picture from the Internet and when I switched off the laptop and started it up again it was always there🤔