There seems to be a very nice toolchain for converting a PDF scan into a searchable PDF with an OCR text underlay. It has been discussed in the german IT magazine c’t: http://heise.de/-2356670 It is hosted on GitHub: https://github.com/fritz-hh/OCRmyPDF I find this very interesting and it would be great addition to Gentoo Linux, but I don’t find the time to write an ebuild at this time. So if OCRtoPDF sounds interesting to you as well and you have the time and the means: please share your ebuild! Thanks.
*** Bug 686648 has been marked as a duplicate of this bug. ***
https://repology.org/project/ocrmypdf/versions
There is an ebuild in guru https://gitweb.gentoo.org/repo/proj/guru.git/tree/app-text/OCRmyPDF