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Compatibility notes
Danbooru native IQDB hash input is not fully compatible; Emalm currently accepts its own signature_hash.
Source-page extraction already resolves many public page URLs, and supported sites can reuse shared public site credentials during source-page resolution; unsupported source pages can still require a direct public media URL.
Source pages that fan out to multiple direct media URLs prefer the first downloadable raster or video candidate before svg/page fallbacks.
Similarity math is Emalm Haar/YIQ DB-backed scoring, not byte-for-byte Danbooru iqdbs output.