Trying to run media import with a object that has a filename which doesn't have a corresponding idno gives this result:
media_import_test.jpg: Skipped media_import_test.jpg from because it already exists
CA 1.4 Schema revision 97
By default the media importer doesn't allow duplicates. The file you're trying to add already exists in the system. We identify potential duplicate by checking the md5 file checksum of the file you're trying to add against all files already stored.
In Providence v1.5 (the code in the develop branch on GitHub) there is a checkbox at the very bottom of the import options screen called "Allow duplicate media?". Check that if you want to import duplicates.
Ok, I see. It could have been a better explanatory text. Now, I thought it was "idno" that was the problem and not the actual image file was similar to that already in the database.