Image Hash Generator Generate perceptual hashes (aHash, dHash, pHash) for image similarity comparison.

What Is Image Hash?

An image hash generator that computes three types of perceptual hashes: Average Hash (aHash), Difference Hash (dHash), and Perceptual Hash (pHash). Unlike cryptographic hashes, perceptual hashes produce similar values for visually similar images, enabling fuzzy matching. aHash compares to mean brightness. dHash compares adjacent pixels. pHash uses DCT frequency analysis for the most accurate similarity detection.

Why Use Image Hash?

• Three hash algorithms for different use cases
• Similar images produce similar hashes
• Resistant to minor edits, resizing, and compression
• Click-to-copy 16-character hex hashes

Common Use Cases

Duplicate Detection

Find near-duplicate images in large collections.

Content Moderation

Identify known images regardless of modifications.

Reverse Image Search

Build perceptual indexes for image search systems.

Copyright Protection

Track image usage across different sizes and formats.

Technical Guide

aHash: Image resized to 8×8 grayscale. Each pixel compared to mean — above=1, below=0. 64-bit hash. dHash: Image resized to 9×8 grayscale. Each pixel compared to its right neighbor. 64-bit hash. pHash: Image resized to 32×32 grayscale. 2D DCT computed on 8×8 low-frequency block. DCT coefficients compared to mean. 64-bit hash. All hashes output as 16-character hex strings. Compare hashes using Hamming distance.

Tips & Best Practices

• 1
  dHash is fastest and good for most comparisons
• 2
  pHash is most robust against edits but slowest
• 3
  Hamming distance < 5 indicates very similar images
• 4
  Generate hashes for both images and compare bit-by-bit

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Frequently Asked Questions

Q How to compare?

Compute hashes of two images and count differing bits (Hamming distance).

Q Which hash to use?

dHash for speed, pHash for accuracy, aHash for simplicity.

Q Hash length?

All produce 64-bit hashes shown as 16 hex characters.

Q Rotation?

Hashes are not rotation-invariant. Rotated images differ.

Q Cryptographic?

No — these are perceptual hashes for similarity, not security.

About This Tool

Image Hash is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.