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DPI is a printing metric.  It doesn't affect screen resolution.  If the file is, say, 6,000px x 4,000px, it's a 24MP image regardless of DPI.  The DPI could be 72 or 300.  It doesn't matter.  

This is an image capture from a 4K video clip at 72 DPI.  It's an 8.2MP (megapixel) image, and was approved for sale here:

stock-photo-sheepshead-fish-archosargus-

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15 minutes ago, Thomas Foo said:

Is it right to assume that whoever buys the 72dpi image is only for web use, not for print?

No.  Look at how scaling an image for print in PhotoShop changes the DPI.  Start with an image at 3840 x 2160 at 72 DPI:

2019-08-18_02-52-25.thumb.jpg.6412e281025f7ab125d3ffa3e77e664e.jpg

Bring it into PhotoShop and print at 100%.  It yields a (roughly) 13" x 7" print (too large for the standard letter (8.5" x 11") paper I had loaded.

2019-08-18_02-54-45.thumb.jpg.5ec3f8379aab642d9556b773d64084a8.jpg

At 100% with some cropping, this image will be sent to the printer at 300 DPI.  But if we scale it to the media:

2019-08-18_02-56-45.jpg.e190c3c61d9d6731f034805fb42d5de7.jpg

The PRINT resolution increases but the image itself is still 3840 x 2160.  Scale it up 400%, and look what happens:

2019-08-18_02-59-25.thumb.jpg.39c54dd90101a2282cdeec201454c495.jpg

The PRINT resolution is 75 DPI, but the image can now be printed on 51" x 28" paper.  Or cropped, as you see it, on standard letter.  The early digital cameras shot 4MP images at 72 DPI and could produce excellent 8"x10" prints.  So yes, 72 DPI (now known as PPI or pixels per inch) can easily produce good prints, because the more important factor is the image resolution.  Here is a 30MP image set to print at 300, 600, and 75 DPI respectively.  Look how all the numbers change except for the image resolution (30MP) itself:

2019-08-18_03-20-28.thumb.jpg.827f0cd1cf5e9ed95255d10e69db9390.jpg

2019-08-18_03-21-33.thumb.jpg.7a91bd4cefe220fad51d1655da39c780.jpg

2019-08-18_03-22-41.thumb.jpg.63b4fc52ce7cd8a52a02fa5c484d3384.jpg

The image resolution remained 6365px x 4243px for every instance above, but scaling for print changed the DPI, which only affects the printed image, not the image file itself.

So again, yes, you can certainly obtain excellent prints from images shot at 72 DPI if there is enough resolution in the image file to begin with.  At 8MP, you can print a 16 x 20 no problem.  

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