Adding a missing tag from the Exif IFD

In the process of parsing and finding duplicate images in a huge library; I came across an Exif tag which could be used to properly identify unique images, in cases where a SHA-256 sum does not help due to differing metadata. The tag in question is 0xA420 (ImageUniqueID) and it is basically a 128-bit ASCII string generated by the device.

For more information on the tag, read: http://www.awaresystems.be/imaging/tiff/tifftags/privateifd/exif/imageuniqueid.html