Description:
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The documentation for exif_read_data() at http://www.php.net/exif_read_data doesn't state whether or not the function validates Exif data before returning it, my guess is not but it should be explicitly stated.

Validation of Exif data would be to check if the contents of a given tag conform to the value it's supposed to hold according to the Exif specification ( see: http://exif.org/Exif2-2.PDF , page 20), for example a tag which should hold a BYTE (according to the spec) should not hold anything besides an 8bit integer, short should not be anything besides a 16 bit unsigned integer and so on.

I'm not suggesting that exif_read_data() does this (if it doesn't) but merely that the documentation be updated to state whether or not it does.