Step 1
Create a bitmap image with size 100x100 with à simple filename.
Sample => "Pergola_folder.bmp" remark => no space or special character.
Step 2
Copy image to library folder => "C:\Cover\XLib\Providers\Cover\Libraries\Conservatories"
Step 3
Edit your "DIRECTORIES.XML" in structure type folder library and put a new markup called "picture".
You can verify into your Cover software.
You can check into Cover provider if you have a 2.3 Cover software version.