pdfsandwich generates "sandwich" OCR pdf files, i.e. pdf files which
contain only images (no text) will be processed by optical character
recognition (OCR) and the text will be added to each page invisibly
"behind" the images.
pdfsandwich is a command line tool which is supposed to be useful to
OCR scanned books or journals. It is able to recognize the page layout
even for multicolumn text.
Essentially, pdfsandwich is a wrapper script which calls the following
binaries: unpaper, convert, gs, and tesseract. It supports
parallel processing on multiprocessor systems.