Where do the AccessData KFF hash libraries come from?
AccessData collects and provides hash values from several government institutions.
NIST (the National Institute of Standards and Technology) produces a collection called the "National Software Reference Library" (NSRL). The NSRL is a large body of hashes computed from application installer programs. Further information about the NSRL can be found at http://www.nsrl.nist.gov/ and http://www.nist.gov/oles/forensics/forensic-database-tech-digital-evidence-table.cfm.
NDIC (the National Drug Intelligence Center) created a collection of hashes called "HashKeeper", which they divided into Alert and Ignore groups. Their Alert sets came largely from prosecuted child pornography cases. NDIC closed its doors in 2012, but some further information can be found at http://www.justice.gov/archive/ndic/.
DHS (the Department of Homeland Security) maintains hash sets of known and suspected child exploitation files found in ICE investigations. Further information can be found at http://www.nist.gov/oles/forensics/forensic-database-tech-digital-evidence-table.cfm.