Digital Photography: Relationship between pixels and 'dpi'

[bobgroh]

Not exactly train stuff but could stand a little explanation on relationship between pixels and dpi (dots per inch). The pictures from my Olympus 1.3 Megapixel camera (hi resolution jpeg format) are 1260 x 800 pixels (or thereabouts). Or slightly bigger than my video monitor screen in what ever mode it is in. I can divide the # pixels by the screen width in inches and that should be the equivalent of 'dots per inch' if each dot is a pixel. But doesn't that make 'dpi' a function of the viewing device rather than the basic digital picture itself? I know the 'dpi' is historically related to the printing world and certainly was used in the early computer printers (i.e. the now ever so ancient '10 dpi' types) but how can I relate, for example, TRAINS request for digital pictures of at least '75 dpi' with the resolution of my (now) old Olympus? Inquiring minds want to know! Thanks.

[eastside]

DPI really has meaning in context with printed or hardcopy output, meaning that for each horizontal or vertical inch there are that number of pixels. I don't know why TRAINS requests "75 dpi" images since one can arbitrarily change the number of pixels/inch in an image editing program.