SUMMARY
FEATURE REQUEST: restrict duplicate image search in Similarity to have one folder or a group of folders as the 'mandatory reference' folder(s), i.e. photos would just be considered duplicate if they exist in the 'mandatory reference' set of folders.  As implemented today, duplicates are also found between folders which are NOT listed in the 'prefer selected folder as reference' because, in the absence of duplicates in the folders selected as reference, Digikam will pick another folder as reference. By implementing mandatory reference folder(s), the photos would only be tagged as duplicates if they DO exist in the mandatory set and Digikam would skip duplicates between non-mandatory folders.

Use case: Allow one-to-many search for duplicates - compare folder 'X' to a list of folders and check if there are duplicates between folder X and the provided list of folders.

SOFTWARE/OS VERSIONS
Windows 10
DigiKam 8.3.0