Create a folder named whatever you want it to be. I recommend
wallpapers in your home folder.
Inside this, create 2 folders:
usr folder, create
share. In that, create
wallpapers. Put your wallpapers there.
DEBIAN folder, create 2 files:
Then, make the control file look like:
Package: package name
Maintainer: your name <your@email>
Version: version number
Depends: whatever it depends on.
Description: a brief description of what your package includes or does.
<blank line here>
Note the blank line at the end, important!
chmod a+r /usr/share/backgrounds/<wallpaper 1>
chmod a+r /usr/share/backgrounds/<wallpaper 2>
chmod a+r /usr/share/backgrounds/<wallpaper n>
Do that for as many wallpapers as you have.
Save all the files.
sudo chown -R root.root ~/wallpapers/
sudo dpkg -b ~/wallpapers wallpaper.deb
Then, you upload this to your PPA. Done!