Originally posted by stevebrot The JPEG is the same regardless of the dpi setting. It exists solely as instructions (hint actually) to the printer indicating intended final dimensions. The printer will up/down sample as is appropriate to make that dpi.
Steve
I suppose it would be good to expand a little. The confusion is mostly the fault of Adobe Photoshop. A generation of graphics professionals were trained to think of image size in terms of dpi. This is great for printing, where dpi is an indication of resolution and there is a direct proportional relationship between that and size, but for digital captures the total number of pixels is the best indicator of resolution.
More pixels = more data = higher resolution
There is a rather complete and (unfortunately) sarcastic discussion at the page linked below.
Dpi, misunderstandings and explanation, what is dpi
What does this mean in practice? It all depends on if and how you print. If you aren't printing, it makes no difference. If you are printing on your home computer, it probably still makes no difference, particularly if you are printing directly from Elements, Lightroom, Photoshop, Paintshop Pro, The Gimp or whatever. Those programs typically work directly with the printer driver to give you whatever dimensions you specify and will up/down sample the image as needed. With most modern cameras and consumer printers you will have enough pixels to print to up to the maximum paper size with reasonable quality.
Where it gets complicated is when you having larger prints done by a print shop or service bureau. The industry standard is 300 dpi on the paper meaning that if you want 9"x6" inch print from APS-C you will have to have 2700 pixels on the long side of the image. That would be about 5 Megapixels with a little cropped off to make it fit. 10"x8" requires 2400px on the short side and a cropped 7 Mpx APS-C image and so on.
Steve