How can I tell if a JPEG has been resized, and do 72 dpi or 300 dpi metadata matter?
Asked 6/27/2017
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I bought two JPEGs from event photo services and want to know whether they were resized or otherwise changed from the camera originals. One file is 3744×5616 from a Canon EOS 5D Mark II and shows 72 dpi. The other is 1488×2240 from a Nikon D70s and shows 300 dpi. Is there a reliable way to use image metadata and known camera specs to tell if a file was resized or cropped? Also, what do these numbers mean for printing, such as around 8×11 inches or larger poster sizes?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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The DPI is insignificant. It means nothing until the image is printed. Cameras almost always just put 72 DPI in the metadata, although on a handful of models it is configurable. Still, no matter what is set there, it will be wrong every time a different print size is used.
The first image is exactly as the camera shoot it. The Canon 5D Mark II is a 21 MP camera and makes images of 5616x3744 pixels at its maximum resolution.
The Nikon D70 is a 6 megapixel camera and is much older. That one produces images of 3000x2000 pixels, so the image has been changed from its original. It is possible it was scaled down but it is even more likely that it simply was cropped. When shooting people, particularly with movement, it is safer to shoot a bit wider and crop after to produce a more compelling image.
Originally by user1620. Source · Licensed CC BY-SA 4.0
user1620
9y ago
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The dpi value in JPEG metadata is usually not useful for judging image quality or whether a file was resized. It mostly affects default print sizing, not the actual captured detail. What matters most is the pixel dimensions.
For your examples:
- The Canon 5D Mark II image at 5616×3744 matches that camera’s full native resolution, so it likely was not downsampled.
- The Nikon D70s normally produces about 3008×2000 pixels, so a 1488×2240 file is not the full original. It was changed somehow—possibly cropped, possibly resized, or both.
Metadata alone usually cannot prove exactly what happened. Comparing the file’s pixel dimensions to the camera’s known native output is the best clue.
For printing, use pixels, not 72 dpi vs 300 dpi metadata:
- 5616×3744 is plenty for a good 8×11 print and can go much larger.
- 1488×2240 is enough for a small print and may still work around 8×11 depending on quality expectations and viewing distance, but it has far less detail for large prints.
In short: ignore the dpi tag, check the pixel count, and compare it to the camera’s native resolution.
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