feat(compare): add face comparison functionality with cosine similarity

README.md

@@ -55,6 +55,35 @@ cargo run --release detect --output detected.jpg path/to/image.jpg
 cargo run --release detect --threshold 0.9 --nms-threshold 0.4 path/to/image.jpg
 ```
 
+### Face Comparison
+
+Compare faces between two images by computing and comparing their embeddings:
+
+```bash
+# Compare faces in two images
+cargo run --release compare image1.jpg image2.jpg
+
+# Compare with custom thresholds
+cargo run --release compare --threshold 0.9 --nms-threshold 0.4 image1.jpg image2.jpg
+
+# Use ONNX Runtime backend for comparison
+cargo run --release compare -p cpu image1.jpg image2.jpg
+
+# Use MNN with Metal acceleration
+cargo run --release compare -f metal image1.jpg image2.jpg
+```
+
+The compare command will:
+1. Detect all faces in both images
+2. Generate embeddings for each detected face
+3. Compute cosine similarity between all face pairs
+4. Display similarity scores and the best match
+5. Provide interpretation of the similarity scores:
+   - **> 0.8**: Very likely the same person
+   - **0.6-0.8**: Possibly the same person
+   - **0.4-0.6**: Unlikely to be the same person
+   - **< 0.4**: Very unlikely to be the same person
+
 ### Backend Selection
 
 The project supports two inference backends:
@@ -106,7 +135,7 @@ The MNN backend supports various execution backends:
 
 - **CPU** - Default, works on all platforms
 - **Metal** - macOS GPU acceleration
-- **CoreML** - macOS/iOS neural engine acceleration  
+- **CoreML** - macOS/iOS neural engine acceleration
 - **OpenCL** - Cross-platform GPU acceleration
 
 ```bash
@@ -179,7 +208,7 @@ MIT License
 Key dependencies include:
 
 - **MNN** - High-performance neural network inference framework (MNN backend)
-- **ONNX Runtime** - Cross-platform ML inference (ORT backend)  
+- **ONNX Runtime** - Cross-platform ML inference (ORT backend)
 - **ndarray** - N-dimensional array processing
 - **image** - Image processing and I/O
 - **clap** - Command line argument parsing