Hello, in ubuntu 18.04. I do not manage to put a photo of my choice for the option "screen locked": I click on settings then I click on "background". then I click on "screen vèrouillé". A window appears I click on image. Another fellow was appearing where I am olgged to click on imags to reach the images saved on my post. but then I can not select an image for it to appear as a locked screen image Is there a command via the terminal to perform?