Does the dpi number reported by camera in JPG have any meaning?

Question

I have two cameras, a 6mpix Panasonic FZ8, and 14mpix Canon A2200.

When I compare shots from two cameras, one of differences I notice is
dpi number that camera reports in JPG info:

• FZ8 reports dpi=72
• A2200 reports dpi=180

What physical meaning can these numbers have? I am at loss for guesses.

I am fairly familiar with notion of dpi in scanning and printing. I can calculate density of pixels on the sensor of the camera. But then, the linear density of pixels on the sensor will be hundreds times larger than number above. So what, if anything, does it mean?

Answer

The values are arbitrary and meaningless, and only serve to confuse people. The EXIF standard seems to imply that if the tag is missing, 72 is the (still-meaningless) default. However, it is apparently mandatory for the TIFF standard, from which the JPEG/EXIF format basically inherits everything. So maybe it has to have some value to properly comply with the standard.

You can still ignore it, though.

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