Why can duplicate photo files have slightly different file sizes?
Asked 4/8/2015
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2 answers
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I’m consolidating old drives and finding many duplicate photos. In a lot of cases the images have the same dimensions and appear identical, but the file sizes differ by a small amount, for example 56 KB vs 58 KB. Does that usually matter when deciding which copy to keep, and what typically causes the size difference between otherwise identical-looking photo files?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
9
If the images actually are duplicates then the additional data is most likely to be metadata which has been added at some point. In other words the files have been modified, although the picture itself has not been touched.
Most likely an automated function in your photo viewing/management software has done it. For example facial recognition which is available in Windows Live Gallery, Picasa and others may have modified the metadata as a background task.
To see what modified them you could examine and compare the metadata between two images using something like exiftool if your curiosity really has to be satisfied.
I'd say if you're unsure then keep the larger file in each case, although whatever was added can probably be recreated by the application if needed, so you shouldn't need to agonise too heavily over which one to keep or lose sleep if you get the wrong one.
Originally by user14028. Source · Licensed CC BY-SA 4.0
user14028
11y ago
0
Generated from our catalog & community — verify before relying on it.
Small size differences between apparently identical photos are usually caused by metadata, not changes to the visible image. Photo software can add or update EXIF/IPTC/XMP data in the background—for example tags, face recognition info, captions, ratings, or other cataloging details—so the file is technically modified even though the picture looks the same.
If you want to confirm that, compare the metadata with a tool like exiftool.
If you’re unsure which copy to keep, keeping the larger file is a reasonable rule of thumb, since it may contain more metadata. That said, the extra data is often application-generated and may be recreatable, so the image itself may be unchanged.
More important long term is having a clear digital asset management workflow: keep originals, keep any edited versions you want to preserve, and be consistent about which drive or folder is your master working library so you know which file is the current version.
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