Automatic indexing and retrieval of crime-scene photographs Katerina Pastra, Horacio Saggion, Yorick Wilks NLP group, University of Sheffield Scene of Crime Information System (SOCIS)

Cambridge 2002 Outline > Application Scenario > Project Overview > SOCIS features > Text-based approaches > Using NLP: > The Indexing mechanism > The Retrieval mechanism > Preliminary system evaluation > Links

Cambridge 2002 Crime Scene Documentation: Current Practices > Scene of Crime Officers:  attend crime scene  photograph the scene  collect evidence (package and label items)  write reports and create indexed photo-album(s)  case-files piled in storage rooms

Cambridge 2002 Examples

Cambridge 2002 IT support for CSI > Crime Investigation requires:  Fast and accurate retrieval of case-related info (and therefore efficient classification of this info)  Identification of “patterns” among cases > IT support for Crime Investigation:  Governmental agencies’ Systems (HOLMES)  Commercial Systems (LOCARD, SOCRATES) (Crime Management and Administration Systems) Needed: “Intelligent” support for Crime Investigation

Cambridge 2002 Project Overview > Domain: Scene of Crime Investigation (SOC) > Scenario: Use of digital photography and speech to populate a central police database with case related information > Objective: Creation of a prototype system that allows for intelligent indexing and retrieval of crime photographs

Cambridge 2002 SOCIS features  Access through the web (JSP application)  Storage of case documentation & meta-information in central database  Automatic indexing of photographs  Automatic retrieval of photographs  Automatic population of official forms

Cambridge 2002

“view of deceased with computer cable removed”

Cambridge 2002 Text-based image indexing & retrieval: approaches Manual assignment of keywords Automatic extraction of keywords (statistics +/ semantic expansion) [Smeaton’96, Sable’99, Rose’00] Extraction of logical form representations (syntactic relations and concept classification) [Rowe’99] Precision and recall increase as indexing terms go beyond keywords capturing relational info

Cambridge 2002 Text-based image indexing & retrieval: problems  “view to the loft” vs. “view into loft”  “position of baby with no bedding”  “position of baby with bedding removed”  keyword barrier  syntactic relations need to be complemented with semantic information Consider:

Cambridge 2002 Pipeline of processing resources: tokeniser  sentence splitter  POS tagger  lemmatizer  NE recognizer  parser  discourse interpreter (+ triple extraction layer) Indexing-Retrieval Mechanism Free text query OntoCrime + KB Indexing terms ARG1 REL ARG2 Query triples ARG1 REL ARG2 matchingmatching captions

Cambridge 2002 Corpus and Domain Model  1200 captions from 350 different crime cases dealt by South Yorkshire Police (text files)  65 captions (transcribed speech experiment) Different lengths but same characteristics: Phrasal constructions, named entities, meta-info, what and where references Domain model = OntoCrime and knowledge base Role = selection restrictions for triples’ arguments and semantic expansion for retrieval

Cambridge 2002 Triple Extraction  17 Relations : AND, AROUND, MADE-OF, OF, ON, WITHOUT etc.  Form of triples: ARG1 REL ARG2  Restrictions and filters for arguments  Rules for captions with multiple relations  Inferences restricted to certain cases

Cambridge 2002 Triple Extraction examples  “body on floor surrounded by blood”  “shot of footprint on top of bar”  “photograph from behind bar of body on floor”  “bottle, gun and ashtray on table”  “footprint with zigzag and target on chair” blood AROUND floor blood AROUND body Body ON floor

Cambridge 2002 Retrieval Mechanism  Allow for free text query  Extract relational facts from the query  Match the query triples with the indexing triples of each captioned photograph  Allow for exact match of arguments or class info ARG1, RELATION, ARG2Class:  If no triples can be extracted, keyword matching takes place with semantic expansion if needed

Cambridge 2002 Preliminary Evaluation  Indexing mechanism evaluation run on 600 captions indicated refinements on the rules (80% accuracy in extracting and inferring triples)  Preliminary usability evaluation with real users: Relational information considered to be an intuitive way for forming queries for image retrieval  Future work: overall evaluation of free text query for image retrieval

Cambridge 2002 Conclusions  Could the SOCIS approach be ported to other domains ?  Thorough testing and experimentation needed  However, it is a corpus-driven approach: Not just an alternative image indexing/retrieval approach,but the one dictated by a real application For more information on SOCIS: