I recently installed Zorin 15.3 and would like to add my favourite backgrounds but having searched for the wallpaper directory etc I cannot find where to put them. 
Solved
You don’t need to save your favourite images to the background folder. You have three choices: Wallpapers ( the pre-installed ones; Pictures (in your /home directory, or solid colours. If you want to add pictures to your wallpaper folder this is either usr | share | backgrounds or usr | share | wallpaers. This might be protected so you would need to open a terminal and then
cd …
cd …
cd usr
cd share
sudo chosen [your username] backgrounds / wallpapers to take ownership.
Next open file explorer browse to the folder you have taken ownership of and paste your pictures there.
N.B. only two dots after cd stupid smartphone thinking I wanted ellipsis!
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