ScanTailor Advanced

Pretty powerful, a lot of options for cleaning scanned images and also processing text and images within the scanned document. It doesn't perform OCR but it leaves the document ready for any OCR recognizer.

The only disadvantage is that it may have some learning curve; but I found this tutorial (not mine btw) quite useful https://www.youtube.com/watch?v=IM1EqJ3MCII

ScanTailor is a promising open source app for deskewing scanned images; for example, to straighten a scanned book page image so that the lines of text are horizontal. Indeed, ScanTailor is able to do that automatically quite well. I tried it on a scanned book project that had 180 scanned pages. All pages came out deskewed properly. However - and this is the fatal problem - it trims away parts of the image as it deskews, and if you continue with its mandatory processing steps, it trims and hacks the pages into bits. There are no overrides to stop it doing this. So basically it cannot be used to scan a book and create a neat digital copy, because the head of the page canvas will be trimmed off to the top of the first line of text, and any photographs bleeding beyond the text block will be trimmed (and the page canvas as well). It also arbitrarily adds white space to the page foot. These are things that of course you want control over, but you can't stop it doing this. I guess if you manually controlled each page you could get a good result, but when you have hundreds of pages, you want an automatic tool, working on each page on-by-one isn't viable. It's such a pity that ScanTailor goes feral on the images after deskewing, because the deskew function itself works so well and so automatically. But in the end, I found it to be an app that I couldn't use.