You have to install tesseract and imagemagick packages. If you use a Debian-based distribution it is as simple as:
$ aptitude install tesseract imagemagick
After that, you have to edit OpenKM.cfg and set the \"Config.SYSTEM_OCR\" parameter to the tesseract binary file. Restart JBoss and OpenKM will make an OCR of uploaded TIFF files.
See OpenKM sources (/src/es/git/openkm/extractor/TiffExtractor.java) for more info.
OpenKM Team ( Be open, my friend! )