PiNet comes with the amazing stars background photograph taken by John Lemieux.

If you want to change it to your own custom background image, the image is stored in 2 places.
/opt/ltsp/armhf/usr/share/images/desktop-base/PiNet.png./opt/ltsp/armhf/usr/share/ldm/themes/raspi/bg.png.If you wish to change either of these images, all you have to do is overwrite them with your new image.
For example, to replace the desktop background
sudo cp /home/myname/myamazingimage.png /opt/ltsp/armhf/usr/share/images/desktop-base/PiNet.png
Note the images must be in PNG format.
##Changing the login screen logo
The default login logo is the Raspberry Pi logo, if you wish to change it, apply the same process as above.
It is stored at /opt/ltsp/armhf/usr/share/ldm/themes/raspi/logo.png.
Make sure your logo is also in PNG format and has transparency enabled!