dhash

A dhash implementation for Deno.

A fast algorithm that allows checking if two images are "kind of" the same (the same source image, slightly modified). Examples:

• A resized, compressed, slightly cropped, or color-altered image compared with the original
• A watermarked image versus it's source
• Meme images (mostly the same template, different text)

It does this by computing a perceptual hash of each image and then using it to compare similarity.

Perceptual hashing is the use of a fingerprinting algorithm that produces a 
snippet or fingerprint of various forms of multimedia.

Based on the "Kind of Like That" article by Dr. Neal Krawetz.

Usage

You can compare dhash values by simply computing the Hamming distance between them:

• A distance of 0 represents an identical, or very similar image
• A distance greater than 10 means that you're most likely dealing with a different image
• A distance between 1 and 10 may indicate that you're dealing with variations of the same base image

const [hash1, hash2] = await Promise.all([
  dhash("./tests/dalle.png"),
  dhash("./tests/dalle-copyright.png"),
]);

console.log(compare(hash1, hash2));

There are also two functions that you may use to display the fingerprint in a non-hash form:

/**
     *  toAscii will return the fingerprint represented as a matrix of
     *  black/white pixels, represented by default through unicode low density
     *  and full blocks, ie:
     *
     *   ██░░██████░░░░░░
     *   ░░██░░░░░░░░░░██
     *   ██░░░░░░████░░██
     *   ░░████░░████░░██
     *   ░░░░░░░░░░░░░░██
     *   ████████░░░░░░░░
     *   ░░░░░░██░░░░░░░░
     *   ░░░░░░░░░░░░░░░░
     * /
    toAscii(hash: string, chars: [string, string]): string

    /**
     * save will render the fingerprint as an 8x8px PNG file with black and
     * white pixels, at the specified path.
     *
     * async save(hash: string, file: string): Promise<void>
     */

License

MIT © Claudiu Ceia