The 240ppi resolution comes from the metadata that your camera attaches to the image. Except for printing purposes, the ppi measurement means absolutely nothing.
Yes, you read that correctly: Unless & until you are going to print, you can COMPLETELY ignore any value you see for ppi.
The following link to a book excerpt (first one I found on a quick search) from books.google.com might shed some light for you about WHY 240 ppi has been chosen as the default value for resolution metadata that carries along with the image output (historically, it seems to have something to do with Epson printers native 360 or 720 D.p.i. printer dot resolution)… <
http://xrl.us/i3dvu> (Link to books.google.com) The relevant info is in the 3rd paragraph on page 42.
Unfortunately, a couple things surrounding that info in the book, in part……are misleading advice. A ppi value has NO bearing whatsoever on an image file’s byte-weight.
The best primer for understanding resolution for images in the digital realmfrom scanner or camera, to working in Photoshop, to scaling and using images online or for videoand when and how it matters, please bookmark, then study as you have time at the following website. It’s helped many thousands of people grasp the core concepts, myself included.
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http://www.scantips.com> Scroll down to the *Start link and begin studying there.
If you only learn one thing, it should be this:"Scan (or photograph) for output.
The only numbers for image dimensions that matter are absolute pixel values for width & height, e.g.: 4000pxW × 3000pxH. A value for ppi (or pp/cm) only comes into play when you want to decide how detailed a printed image needs to be at a specific size as measured in inches (or centimeters.)"And deciding what resolution value to use when printing via various hardware is another issue all its own.