The image parameters control where the thumbnails are sourced for the OPAC containers (with some exceptions). You can set up multiple entries which will be looked at by the OPAC page JavaScript in the order they are saved, with the first successful one being used.
A source will only be used if the URL domain and path specified includes a placeholder for a record's identifying data, and the data exists, for example #ISBNNO, #UPC, #OCLC.
To add, edit or delete the parameters for an image source:
If you mix http and https sources, you will get a warning as https pages should not make any calls to http servers.