Finding captions in PDF-documents for semantic annotations of images

The Portable Document Format (PDF) is widely-used in the Web and searchable by search engines; but only for the text content. The goal of this work is the extraction and annotation of images in PDF-documents, to make them searchable and to perform semantic image annotation. The first step is the extraction and conversion of the images into a standard format like jpeg, and the recognition of corresponding image captions using the layout structure and geometric relationships. The second step uses linguistic-semantic analysis of the image caption text in the context of the document domain. The result on a PDF-document collection with about 3300 pages with 6500 images has a precision of 95.5% and a recall of 88.8% for the correct image captions.