Which image to keep -- Similarity scan and different file sizes

[Carol C. Kankelborg]

I ran the Similarity tool with range 99–100% across my whole library. It detected some photos that differ in size, but it is not clear to me which to keep. I must have imported them directly from my camera (Nikon D5600) twice at different times. I moved one to an album of photos from my vacation and the other I left in the album it was imported into. I don’t understand why they would have different file sizes. 

The newer import file that I put into the vacation album is larger than the older one. I zoom in as far as I can in Preview mode and flip back and forth between the two photos and cannot detect a difference, suggesting the JPG compression is the same. 

Here is the result of doing an exiftool comparison between one pair of images. In DigiKam, it lists the Size for the larger image as 14.1 MiB (14,756,434) and the smaller as 12.3 MiB (12,873,885), which do not match the sizes from exiftool. 

I would rather keep the file already in the vacation album, but not if it has a lossier compression than the larger file. I welcome any explanation for what I am seeing and what the reason for the file size might be.

Thanks,
Carol



Shalom-cckborg $ exiftool -diff CCK_7897.JPG ..//Camera\ Import/2024-08-15/109D5600/CCK_7897.JPG 
======== diff < ..//Camera Import/2024-08-15/109D5600/CCK_7897.JPG > CCK_7897.JPG
< [System]        Directory                       : ..//Camera Import/2024-08-15/109D5600
>                                                 : .
< [System]        File Size                       : 15 MB
>                                                 : 13 MB
< [System]        File Modification Date/Time     : 2023:11:17 10:38:32-07:00
>                                                 : 2023:11:19 17:07:02-07:00
< [System]        File Access Date/Time           : 2025:01:18 04:53:40-07:00
>                                                 : 2025:01:18 21:36:07-07:00
< [System]        File Inode Change Date/Time     : 2025:01:15 21:31:46-07:00
>                                                 : 2025:01:06 20:01:39-07:00
< [File]          Image Width                     : 6000
>                                                 : 4000
< [File]          Image Height                    : 4000
>                                                 : 6000
< [File]          Y Cb Cr Sub Sampling            : YCbCr4:2:2 (2 1)
>                                                 : YCbCr4:4:0 (1 2)
> [File]          Current IPTC Digest             : 1e94c722fc098f69f3aa0d01b303732c
< [IFD0]          Orientation                     : Rotate 90 CW
>                                                 : Horizontal (normal)
> [IFD0]          Processing Software             : digiKam-8.1.0
> [IFD0]          Image Width                     : 4000
> [IFD0]          Image Height                    : 6000
< [ExifIFD]       Exif Image Width                : 6000
>                                                 : 4000
< [ExifIFD]       Exif Image Height               : 4000
>                                                 : 6000
< [IFD1]          Thumbnail Offset                : 18296
>                                                 : 18284
< [IFD1]          Thumbnail Length                : 9886
>                                                 : 4909
< [MPImage2]      MP Image Start                  : 13713920
>                                                 : 13661039
< [MPImage3]      MP Image Start                  : 13812224
>                                                 : 13759343
< [Composite]     Image Size                      : 6000x4000
>                                                 : 4000x6000
> [XMP-x]         XMP Toolkit                     : XMP Core 4.4.0-Exiv2
> [XMP-tiff]      Image Width                     : 4000
> [XMP-tiff]      Image Height                    : 6000
> [XMP-tiff]      Orientation                     : Horizontal (normal)
> [XMP-tiff]      Software                        : digiKam-8.1.0
> [XMP-exif]      Exif Image Width                : 4000
> [XMP-exif]      Exif Image Height               : 6000
> [IPTC]          Originating Program             : digiKam
> [IPTC]          Program Version                 : 8.1.0