Actually, you don't have to add manually your 80 wallpapers. I wrote a script to do that (I have a lot of wallpapers I wanted to add to the appearance menu too ).
This is the script:
All you have to do is put it in a .sh text file and run it in a terminal with something like
# This script creates an xml file that you can
# put on /usr/share/gnome-background-properties (if you want wallpapers entrys to ALL users, requires administrator rights)
# or in /home/userA/.local/share/gnome-background-properties (if you want it only for userA).
# (Realize that the script it's supposed to be runned like this: sh namescript FOLDER/OF/PICTURES/DIRECTION/).
# Don't forget the last "/".
# This script creates a file named my-wallpapers.xml.
# The file will have the xml code that Ubuntu (Gnome) identifies when it search for backgrounds.
# ATTENTION: The file generated will NOT include hidden folders NOR sub-folders pictures.
# ATTENTION: The file will include xml code for EACH file, so only put pictures in that folder.
echo '<?xml version="1.0" encoding="UTF-8"?>' >> "$xmlFile"
echo '<!DOCTYPE wallpapers SYSTEM "gnome-wp-list.dtd">' >> "$xmlFile"
echo '<wallpapers>' >> "$xmlFile"
# For each file in the folder ingresed by the user, it wll create an xml entry.
for img in "$1"*; do
# We'll declare a variable with the entire name of the image (extention included). It will be used to declare the next variable.
# We'll declare a variable with the name without the extention. It will be the name in the appearance menu
Name=$(echo "$CompleteName" | cut -d "." -f 1)
echo " <wallpaper>" >> "$xmlFile"
echo " <name>$Name</name>" >> "$xmlFile"
echo " <filename>$img</filename>" >> "$xmlFile"
echo " <options>zoom</options>" >> "$xmlFile"
echo " <pcolor>#000000</pcolor>" >> "$xmlFile"
echo " <scolor>#000000</scolor>" >> "$xmlFile"
echo " <shade_type>solid</shade_type>" >> "$xmlFile"
echo " </wallpaper>" >> "$xmlFile"
echo '</wallpapers>' >> "$xmlFile"
echo "The file has been created with the pictures in «$1»"
be aware of the last "/". And it's done!
sh your-file.sh your/pictures/folder/
If you want the wallpapers to be able only in your appearance menu you can put the xml file in your local folder (./local/share...) as I mentioned in the script.
You can manage to convert the script to a Slideshow creator too with some little changes.
I hope it'll help some people.