@linuxuser701 If your question relates to the specific name of the background
/usr/share/backgrounds/warty-final-ubuntu.png
That is hard coded so you can’t change the name. To achieve placing your own image as background you can rename the images. I strongly suggest that your image is a .png. You may use gimp to change a jpg image to png by using the export feature.
sudo mv /usr/share/backgrounds/warty-final-ubuntu.png /usr/share/backgrounds/warty-final-ubuntu.png.org
sudo cp YOUR COMPLETE IMAGE NAME /usr/share/backgrounds/warty-final-ubuntu.png
sudo update-grub
Regards,
Pete