watermarker generates watermark codes and writes them to the IPTC field "SpecialInstructions"

IWApertureAccess provides access to various parts of the Aperture library:

GetSelectedPhotos gets the list of photos from the Aperture selection.
GetDatabase returns the path to the database.
GetLibrary returns the path to the current Aperture library.
WriteIPTC writes info to an IPTC field of the given photo.
GetPreview returns the path to the aperture preview