Usually, when importing photos into a Lightroom catalog, the Do No Import Duplicates is checked on. The question is what’s a duplicate? Everybody in their right mind would assume that 2 duplicate photos are 2 identical photos. It turns out that for programmers, 2 identical photos are not the same as 2 identical files.

What Lightroom really mean is 2 identical files. What are identical files?

  • The same name like: charlie-20111129-1234
  • The same file extension like: .cr2

This means that charlie-20111129-1234.cr2 and charlie-20111129-1234.jpg are not identical files. Both will be imported into the Lightroom catalog. But the JPEG file can be treated as an adjunct and not be displayed.

This means that charlie-20111129-1234.cr2 and charlie-20111129-1234.tif are not identical files. Both will be imported into the Lightroom catalog.

This means that charlie-20111129-1234.cr2 and charlie-20111129-1234.psd are not identical files. Both will be imported into the Lightroom catalog.

This means that charlie-20111129-1234.cr2 and charlie-20111129-1234.dng are not identical files. Both will be imported into the Lightroom catalog.

Lightroom only looks at the complete name of the file to decide if the “newly displayed to be imported” file is a duplicate of an existing photo into the catalog.

  • The keyword here is suspected.
  • The standard way of checking for duplicates in the computer world is to do a checksum by hashing the file and see if the checksums are identical.
  • Checksums would not work in this case because the files are different. The raw image is 27.1Mb, the JPEG image is 6.7Mb, the TIFF image is 39Mb and the PSD image is 37Mb. It’s the same photo but all these images are different formats and different contents.