Quick and dirty PDF OCR in Fedora 21

Every so often you wind up with a scanned PDF of mostly text. Performing OCR allows you to both search and select text in the document. Usually for one-off scans, a quick OCR is sufficient (no training, no skew correction, etc.). For those cases, I usually recommend pdfocr. Unfortunately for Fedora users, pdfocr uses PDFtk (which Fedora does not package due to it's dependence on gcj), and ExactImage, which no longer has a maintainer. Read on for a quick work around.


The first issue is PDFtk. Since pdfocr already uses Poppler for converting PDF files to PPM before feeding them to an OCR engine, I forked pdfocr to use Poppler in place of PDFtk for it's PDF split and join operations.

Second issue is the packaging of ExactImage which pdfocr uses to merge the hOCR files generated by the OCR engine with the PPM files generated from the PDFs. I suspect ExactImage no longer has a package maintainer since it needs to be patched to support the libpng and giflib versions used by Fedora. I ported (stole wholesale) the patches used by Debian, and put them together to build the necessary RPM.

I put the RPMs for my pdfocr fork and ExactImage in my pdftools copr repository. Simply enable the repo, install pdfocr, then you can quickly OCR a PDF with:

pdfocr -i [input].pdf -o [output].pdf

I find the CuneiForm OCR tool does a better job than Tesseract (likely due to the default configuration, and not the actual quality of the OCR engine), add the '-c' option if you want to try it. As with all things, you mileage may vary!