There have been many threads on this subject. You can just search for the phrase "dots per inch" and find many of them. But here is a link to a post by RG that goes into some detail:
http://www.glamour1.com/forums/tech-...nch#post237468
The bottom line is that the camera takes a photo using its built in resolution or a resolution that you set it to. For example, a camera may take the photo at 3000x2000 pixels. What is the DPI. Well there isn't any! At that point we don't know what the final use of the photo will be so you can't specify DPI meaningfully. So the camera maker just sticks into the "m e t a" data of the photo some arbitrary value like 240 dpi, or 216 dpi, or whatever. Then your Photo editing program may arbitrarily set it to some other value. But you can change the value whenever you want. The photo doesn't change at all when you change the dpi setting.
Cheers,
rfs