How do I find all image-based PDFs?

Question

I have many PDF documents in my system, and I notice sometimes that documents are image-based without editing capability. In this case, I do OCR for better search in Foxit Phan

Answer 1

Purely from OCR field, we can use the Hough transform to find the biggest square in a page, then we calculate the ratio of its area and the whole area. If the ratio is low, we can think this page is slopping. Finally, statistics proportion of slopping pages and the page sum can indicate whether this PDF is scanned PDF.

I know the process is very slow and the proportion is difficult to determine. ^-^