I am so glad I read the OP. To me, the big news here is "FlatCV", the author's computer vision library.

Why it interests me:

1. A practical and elegant approach to scanning real-world documents like receipts, invoices, and letters. These usually have folds, curvature, and wrinkles, and general-purpose scanning tools do a poor job.

2. It's written in C.

3. It takes output quality seriously, finding color thresholds suitable for printed matter carefully and building PNG images instead of throwing you into a generic jpg pipeline.

Thank you for writing this software and also the introduction! Will definitely read further.