Today’s Question: I have always assumed that “Don’t Import Suspected Duplicates” only applied to photos that had been previously imported. Your response to the question [from yesterday] implies that Lightroom Classic recognizes identical copies of photos that have not yet been imported. What metadata is used to identify the duplicates? How to Lightroom Classic determine which photos get imported versus not? Will photos be deemed duplicates if they have slightly different file names?
Tim’s Quick Answer: Duplicates can be detected even when importing with the “Add” option in Lightroom Classic, though there are some limitations that can cause problems depending on how the files were renamed.
More Detail: Lightroom Classic determines which photos are duplicates by evaluating the original filename (which is not necessarily the same as the current filename), the capture date and time, and the file size. When it comes to the filename, however, in some cases a duplicate will still be detected if the filename doesn’t match, depending on how the file had been renamed.
When you use Lightroom Classic to rename a photo, the original filename will be added to the “Original Filename” field in metadata. Other software such as Adobe Bridge includes this option as well. When an original filename is found in this field, Lightroom Classic uses that as the filename being evaluated to determine duplicates.
If you had renamed the photos using software that preserves the original filename in the Original Filename field of metadata, then Lightroom Classic would still be able to accurately detecting duplicates. If, however, you were to manually rename the photos such as through the operating system, then the photos would not be identified as duplicates due to the filename mismatch.
The context of the original question in yesterday’s Ask Tim Grey eNewsletter was a photographer who had been previously using Lightroom Classic, but who wanted to start fresh with a new catalog after replacing their computer. Therefore, any renaming would have likely been done using Lightroom Classic, and the duplicates would have been detected accurately.
When duplicates are detected during the import of a large number of photos using the “Add” option in the Import dialog, you don’t have any control over which of the files will be considered originals versus duplicates. Therefore, if there is any doubt about the status of the two versions of photos being imported, you may want to import all of them with the “Don’t Import Suspected Duplicates” checkbox turned off, and then deal with identifying duplicates with a more manual process in your workflow.