Up until a couple months ago, if I changed my wallpaper/background image, I could choose between tile, zoom, centre, scale, fill or span. These options no longer appear in GUI for changing the background image.
I am using Ubuntu 17.10.
The default GUI option to change wallpaper (accessible from Settings application) doesn't offer these options. I believe the idea is that average users usually download (or crop) wallpapers that fit their desktop background perfectly (i.e. images with the correct aspect ratio based on the screen resolution).
As an alternative, you may use (GNOME) Tweaks to get those extra options. To install it first run
sudo apt install gnome-tweaks
Then launch Tweaks and go to the 'Appearance' section on Ubuntu 18.04 and later (or the 'Desktop' section on Ubuntu 17.10). You'll get options to adjust the background and lock screen images.
You can use a terminal tool called
gsettings list-schemas-- among others you will get,
org.gnome.desktop.background: Option 1
org.gnome.desktop.screensaver( for lockscreen, just in case ) : Option 2
gsettings list-recursively org.gnome.desktop.background, must try!
You will what different options are supported by the schemas with there default values, you'll get something like this,
org.gnome.desktop.background picture-options 'zoom'
now if you want to know what are the other values supported by the options, other than default, do, for example.,
gsettings range org.gnome.desktop.background picture-options
'none'(blank screen/ color black),