Photo Metadata can be traced back far beyond modern digital photography, (notes scribbled on the frame of a slide mount), but the seeds were sown for modern digital metadata in 1990 with the release of the IPTC’s (International Press Telecommunications Council) general purpose Information Interchange Model (IIM).
Modern digital metadata took root with the release of Adobe Photoshop 95, which added support for 20 of the IIM fields in a standardized manner called the Image Resource Block (IRB). Shortly after that first version of the Exif (Exchangeable Image File Format) standard for technical image data was released. Adobe introduced XMP (Extensible Metadata Platform) in 1991 in response to limitations with the IPTC/IIM format, and to unify all this data into one common place. Further updates appeared in 2005 (IPTC Core) and 2008 (IPTC Extensions and PLUS) that added additional fields such as country codes and model release information.
With all these ways to represent data, some problems have emerged. The legacy IRB and Exif blocks remain for backwards compatibility. Length restrictions applied to fields in the legacy blocks do not apply in XMP (the IRB Byline field is limited to 32 bytes). Extended character sets are properly supported in XMP by its XML root, but are poorly or not supported in legacy blocks. Similar data can now exist in multiple locations, for example the IIM Date and Time Created (2:55/2:60) fields should contain the same value as Exif DateTimeDigitized (x9004), and both of those should match the XMP values for the XMP:CreateDate and EXIF:DateTimeDigitized fields. With all these sources of data, it’s easy to see things lose sync.
This metadata can be very helpful if it still exists. Is there a copyright on the picture? When was a picture taken? The date created displayed by your computer may tell you, but if that file was sent over the internet, that will likely show when it arrived. Fortunately one of those fields mentioned above will help.
The GPS data that may be embedded in the Exif data is a wonderful tool, but it can raise concerns if that data falls into the wrong hands. When an image is transferred over Skype, the GPS data is removed, unfortunately it also removes all the IPTC and XMP information. If your copyright notice doesn’t exist in the Exif data, a new risk is introduced.
A recent promo for a smartphone proclaimed it could take pictures “like this”. A look at the Exif data of the picture indicated that a $2600 camera with a $1900 lens was used to take that picture. While it was never stated that the phone was used to take the picture, it was an embarrassment. But the Exif data does not lie.