I see that i can change the login screen image in System Settings. But in that System Settings there is no option to change the login screen background image and lock screen background image.
But u can change the login screen and lock screen background image.
Lets pick in which image you want to replace in the lock screen background
for example, lets take Big Buck Bunny.jpg download the image and save it in your home folder.
after that follow this steps:
cd /usr/share/wallpapers/Elarun/contents/images cd ls
it shows 2560×1600.png which is current background image. let’s take a backup for that image.
sudo cp 2560x1600.png current-background.jpg
after that copy your downloaded image
sudo cp /home/ubuntu/Big Buck bunny.jpg /usr/share/wallpapers/Elarun/contents/images cd /usr/share/wallpapers/Elarun/contents/images sudo mv Big Buck bunny.jpg 2560x1600.png
for cross verification open a browser and type this URL
to lock your screen and you can see your customized image now.
I hope you this blog is helpful for you 😀