Exif
PHP Manual

Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

EXIF_USE_MBSTRING (integer)
This constant have a value of 1 if the mbstring is enabled, otherwise the value is 0.

The exif_imagetype() lists several related built-in constants.


Exif
PHP Manual