AFCP is a specification which allows meta information (including IPTC) to be appended to the end of a
file.
It is a poorly designed protocol because (like TIFF) it uses absolute offsets to specify data locations.
This is a huge blunder because it makes the AFCP information dependent on the file length, so it is
easily invalidated by image editing software which doesn't recognize the AFCP trailer to fix up these
offsets when the file length changes. ExifTool will attempt to fix these invalid offsets if possible.
Scanning for AFCP information may be time consuming, especially when reading from a sequential device,
since the information is at the end of the file. In these instances, the ExifTool FastScan option may be
used to disable scanning for AFCP information.