PrasannaBAImodel/license-plate-keypoint-detection

License Plate Keypoint Detection

A fine-tuned YOLOv8m-Pose model that detects vehicle license plates and precisely localizes their 4 corner keypoints (top-left, top-right, bottom-right, bottom-left). Designed for downstream tasks like logo replacement, plate anonymization, and perspective-corrected OCR.

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Model Details

Property	Value
Base Model	YOLOv8m-Pose (Ultralytics)
Task	Object Detection + Keypoint Estimation
Classes	1 (Plate)
Keypoints	4 corners per plate (TL, TR, BR, BL)
Input Size	640 × 640 px
Model Size	~101 MB
Framework	PyTorch / Ultralytics

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Performance Metrics

Evaluated on the held-out validation set (24 images):

Metric	Value
Box Precision	0.977
Box Recall	0.947
Box mAP@50	0.9875
Box mAP@50-95	0.8412
Pose Precision	0.934
Pose Recall	0.898
Pose mAP@50	0.9264
Pose mAP@50-95	0.9137

Model fully trained for all 150 epochs, achieving best-in-class performance at the final checkpoint.

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Training Details

Parameter	Value
Epochs	150
Batch Size	16
Image Size	640 × 640
Optimizer	SGD (auto)
Learning Rate	0.01 → 0.01
Momentum	0.937
Weight Decay	0.0005
Pose Loss Weight	12.0
Keypoint Object Loss	2.0
Warmup Epochs	3
Augmentations	Mosaic, HSV, Flip-LR, Scale, Shear, Rotation
Device	CUDA GPU

Dataset

• Source: Roboflow — license-plate-new dataset (v3)
• License: CC BY 4.0
• Train: 19000 images
• Validation: 2400 images
• Test: 2400 images
• Annotation: YOLO Pose format, 4 keypoints per plate (x, y, visibility)

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Quick Start

Installation

pip install ultralytics opencv-python numpy

Basic Inference

from ultralytics import YOLO
import cv2

# Load model
model = YOLO("license_plate_keypoint.pt")

# Run inference on an image
results = model("car.jpg", conf=0.25)

for result in results:
    if result.keypoints is not None:
        for kpts in result.keypoints:
            # kpts.xy shape: [4, 2]  — (x, y) for each of the 4 corners
            corners = kpts.xy[0].cpu().numpy()
            print("TL:", corners[0])
            print("TR:", corners[1])
            print("BR:", corners[2])
            print("BL:", corners[3])

Using the Full Inference Pipeline

from inference import LicensePlateKeypointDetector

detector = LicensePlateKeypointDetector("license_plate_keypoint.pt")

# Detect keypoints only
result = detector.detect("car.jpg")
if result["success"]:
    print("Keypoints:", result["keypoints"])
    print("Confidence:", result["confidence"])

# Detect and blur the plate
blurred = detector.blur_plate("car.jpg", output_path="blurred.jpg")

# Detect and replace with a logo
replaced = detector.replace_logo("car.jpg", "logo.png", output_path="out.jpg")

Batch Processing

from inference import LicensePlateKeypointDetector
from pathlib import Path

detector = LicensePlateKeypointDetector("license_plate_keypoint.pt")

for img_path in Path("input_images").glob("*.jpg"):
    result = detector.detect(str(img_path))
    if result["success"]:
        print(f"{img_path.name}: {result['keypoints']}")

Video Processing

from inference import LicensePlateKeypointDetector

detector = LicensePlateKeypointDetector("license_plate_keypoint.pt")
detector.process_video("input.mp4", output_path="output.mp4", blur=True)

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Keypoint Order

The model outputs 4 keypoints per detected plate in this fixed order:

0: Top-Left     (TL)
1: Top-Right    (TR)
2: Bottom-Right (BR)
3: Bottom-Left  (BL)

Each keypoint has (x, y, visibility) values. Visibility > 0.5 means the point is reliably detected.

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Use Cases

• Plate Anonymization — Blur or mask license plates for privacy compliance
• Logo Replacement — Replace plates with custom logos using perspective transform
• OCR Pre-processing — Extract and warp plate regions for accurate text recognition
• Dataset Annotation — Auto-annotate corner keypoints for further training
• Traffic Monitoring — Track vehicle plates in video streams

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Limitations

• Trained primarily on clear, front-facing license plate images
• Performance may degrade on heavily occluded, night-time, or extreme-angle plates
• Best results at image resolution ≥ 640px
• Optimized for standard rectangular license plates

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Files

File	Description
license_plate_keypoint.pt	Fine-tuned YOLOv8m-Pose model weights (~101 MB)
inference.py	Full inference pipeline with blur, logo replacement, video support
requirements.txt	Python dependencies
config.json	Default inference configuration

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Citation

If you use this model, please cite:

@misc{prasanna2024licenseplatepose,
  title   = {License Plate Keypoint Detection using YOLOv8 Pose},
  author  = {Prasanna B},
  year    = {2025},
  publisher = {Hugging Face},
  url     = {https://huggingface.co/PrasannaBAImodel/license-plate-keypoint-detection}
}

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License

This model is released under the Apache 2.0 License.
Base model (YOLOv8) is © Ultralytics, released under AGPL-3.0.
Training data from Roboflow under CC BY 4.0.