After I did backup and restore of the course, background image of the certificate disappeared. I had to manually edit the certificate, load template that was already loaded and save certificate again. That's not a big issue if you do manual backup/restore but if you want to automate the process for large number of courses, for example using web services API, this becomes the big issue. We used Moodle online courses on our university to generate certificate of completion for our classroom short courses. So we made a Moodle course as a template that we want to duplicate using web services API for each offline course that we have. A lot of courses generates a lot of manual work.
Any help in resolving the issue would be appreciated. I know this involves some programming. Author of the plugin would do it easily I suppose. I'm not a hardcore programmer but with some directions from experienced Moodle developer, maybe I could help as well.