[magick-users] Despeckling images for OCR and anti-spam purposes

[Kelly Jones]

Spammers are starting to put "speckles" in their images to defeat
OCR-scanning plugins such as FuzzyOCR.

I thought ImageMagick's -despeckle option would help, but it doesn't
seem to, not even when applied multiple times, not even in conjunction
with -monochrome.

I want a filter that does this for each pixel X:

1) if any of X's 8 neighbor pixels is the same color, turn X black
2) otherwise, turn X white

Can some combination of options to convert do this?

I realize that:

1. This will only work w/ indexed-color images (eg, GIFs) and not JPEGs, etc.
2. Spammers will soon work around this, so this is just a short-term bandage.
3. I could write something in libgd to do this (blech!)

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