How SmartHash
Authenticates Your Media
Six steps from capture to permanent blockchain record. SmartHash runs entirely on your device — fast, private, and forensically sound.
Download the App
Install eWitness from Google Play on your Android device. It integrates seamlessly with your camera.
Capture Media
Take photos or record videos using the eWitness app just as you would with your regular camera app.
SmartHash is Computed
The SmartHash algorithm converts your image to grayscale, applies a 7×7 noise-reduction filter, resizes it to 32×32, and runs a Discrete Cosine Transform (DCT). The top-left 8×8 DCT coefficients are quantized into a compact 192-bit hash fingerprint — all on-device, instantly.
Blockchain Registration
The SmartHash fingerprint is sent to a distributed blockchain ledger. An immutable, timestamped transaction record is created. The transaction ID is stored in the media file's EXIF metadata.
Proof is Permanent
The blockchain record cannot be altered or deleted. Your media now carries a verifiable certificate of origin, capture time, and authenticity.
Share & Verify
Share your media with confidence. Anyone who receives the file can look up the transaction ID on the public blockchain and verify that the content has not been tampered with since capture.
Three Versions,
One Standard
eWitness uses the SmartHash algorithm family, published at ACM CIKM 2024. Each variant offers a different trade-off between speed and detection accuracy.
SmartHash
Hashes the whole image as a single unit. Fastest and most balanced option — ideal for real-time mobile use.
SmartHash Non-Overlapping
Divides the image into 4 non-overlapping blocks and concatenates their hashes. Improves localization of tampered regions.
SmartHash Overlapping
Divides the image into 9 overlapping blocks. Highest accuracy and specificity — best for forensic and evidentiary use.
SmartHash runs up to 33× faster than Apple's NeuralHash (288M cycles) and 56× faster than Microsoft's PhotoDNA (493M cycles) — making it uniquely suited to mobile deployment.
What Makes SmartHash Different?
DCT-Based Perceptual Hashing
SmartHash extends the widely used pHash algorithm using a Discrete Cosine Transform. The image is converted to grayscale, filtered with a 7×7 kernel, resized to 32×32, and the top-left 8×8 DCT coefficients are extracted as a 64-element vector — capturing the perceptual essence of the image.
8-Bin Quantization
Unlike pHash which uses a single binary threshold, SmartHash uses 8-bin quantization (3 bits per coefficient), producing a 192-bit hash. This finer granularity lets SmartHash distinguish between benign content-preserving edits (compression, brightness) and malicious content-changing tampering (object addition or removal).
Normalized Hamming Distance
Two SmartHash fingerprints are compared using Normalized Hamming Distance (NHD). CP-modified images cluster at low NHD values; tampered images fall in the mid range; entirely different images land at high NHD. Dual thresholds (τ ≈ 0.09 and τ₁ ≈ 0.38) enable three-way classification: authentic, tampered, or unrelated.
Performance Across 5 Datasets
Results from the ACM CIKM 2024 paper. SmartHash Overlapping achieves the highest overall accuracy.
| Dataset | CP Precision | Sensitivity | CC Precision | Specificity | Accuracy |
|---|---|---|---|---|---|
| SmartHash Overlapping (Best Overall) | |||||
| CASIA 2.0 | 98.18% | 94.38% | 96.87% | 92.45% | 94.03% |
| Photoshop Battle | 98.02% | 98.02% | 98.30% | 97.01% | 97.01% |
| IMD 2020 | 99.23% | 98.83% | 99.43% | 99.28% | 99.45% |
| DEFACTO Copy-Move | 98.18% | 85.67% | 99.32% | 92.45% | 89.87% |
| COCO Splicing | 95.01% | 83.52% | 98.33% | 92.76% | 93.89% |
SmartHash Overlapping consistently outperforms Apple's NeuralHash and Microsoft's PhotoDNA across all three well-balanced datasets, while running significantly faster on single-core hardware.
Verifying Authenticity
Anyone can independently verify media captured with eWitness:
Receive the media file from the creator
Read the SmartHash transaction ID from EXIF metadata
Look up the transaction on the public blockchain
Confirmed origin, timestamp, and authenticity
Ready to Try SmartHash?
Download eWitness for free and start capturing forensically authenticated media today.