From: Dennis Boone <drb(a)msu.edu> * Don't use JPEG 2000 and similar compression algorithms that try to re-use blocks of pixels from elsewhere in the document -- too many errors, and they're errors of the sort that can be critical. Even if the replacements use the correct code point, they're distracting as hell in a different font, size, etc.

* OCR-under is good. I use `ocrmypdf`, which uses the Tesseract engine.

* Bookmarks for pages / table of contents entries / etc are mandatory. Very few things make a scanned-doc PDF less useful than not being able to skip directly to a document indicated page.

* I like to see at least 300 dpi.

* Don't scan in color mode if the source material isn't color. Grey scale or even "line art" works fine in most cases. Using one pixel means you can use G4 compression for colorless pages.

* Do reduce the color depth of pages that do contain color if you can. The resulting PDF can contain a mix of image types. I've worked with documents that did use color where four or eight colors were enough, and the whole document could be mapped to them. With care, you _can_ force the scans down to two or three bits per pixel. * Do insert sensible metadata. * Do try to square up the inevitably crooked scans, clean up major floobydust and whatever crud around the edges isn't part of the paper, etc. Besides making the result more readable, it'll help the OCR. I never have any luck with automated page orientation tooling for some reason, so end up just doing this with Gimp.