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 PhantomPDF where you can do OCR in multiple files. I would like to find all PDF documents of mine which are image-based. I do not understand how the PDF reader can recognize that the document's OCR is not textual. There must be some fields which these readers access. This can be accessed in terminal too. This answer gives open proposals how to do it in the thread Check if a PDF file is a scanned one: Your best bet might be to check to see if it has text and also see if it contains a large pagesized image or lots of tiled images which cover the page. If you also check the metadata this should cover most options. I would like to understand better how you can do this effectively, since if there exists some metafield, then it would be easy. However, I have not found such a metafield. I think the most probable approach i…

Accepted Answer

Being late for the party, here's a simple solution implying that pdf files already containing fonts aren't image based only:

```
find ./ -name "*.pdf" -print0 | xargs -0 -I {}      \ 
    bash -c 'export file="{}";                          \
    if [ $(pdffonts "$file" 2> /dev/null | \
    wc -l) -lt 3 ]; then echo "$file"; fi'
```

- pdffonts lists all embedded fonts in a PDF file. If the contains searchable text, it also must contain fonts, so pdffonts will list them. Checking if result has less than three lines is because pdffonts' header is 2 lines. So all results lower than 3 lines don't have embedded fonts. AFAIK, there shouldn't be false positives altough this is more a question to ask pdffonts developers.

As one-liner

```
find ./ -name "*.pdf" -print0 | xargs -0 -I {} bash -c 'export file="{}"; if [ $(pdffonts "$file" 2> /dev/null | wc -l) -lt 3 ]; then echo "$file"; fi'
```

Explanation: `pdffonts file.pdf` will show more than 2 lines if pdf contains text. Outputs filenames of all pdf files that don't contain text.

My OCR project which has the same feature is in Github deajan/pmOCR.

How do I find all image-based PDFs?

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