imageguard

Validate images before AI pipelines.

imageguard is a lightweight Python library that checks whether an image is good enough to feed into an AI pipeline — OCR, background removal, upscaling, dataset training, or any model that is sensitive to image quality.

No image-processing knowledge required. Pass in a path. Get back a decision.

from imageguard import validate

result = validate("photo.jpg")

if not result.ok:
    print("Reject:", result.reason)  # "blurry"
else:
    print("Score:", result.score)    # 0.87

Used in production at changeimageto.com — the image quality checker tool that processes thousands of images per day.

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Install

pip install imageguard

For URL support (optional):

pip install "imageguard[url]"

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The result object

result.ok        # bool   – True if the image passes all checks
result.reason    # str    – primary issue (empty when ok=True)
result.issues    # list   – every detected issue
result.score     # float  – 0.0 (worst) → 1.0 (best)

Possible issues

Value	Meaning
blurry	Image is out of focus
low_resolution	Too few pixels for reliable processing
noisy	Excessive visual noise
pixelated	Block artefacts or aggressive upscaling
compressed	Severe JPEG compression artefacts
underexposed	Image is too dark
overexposed	Image is too bright / washed out
clipped	Large portions are pure black or white
bad_exposure	General lighting issue

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Input formats

validate() accepts a file path, a URL, or a numpy array:

from imageguard import validate
import numpy as np

# File path
result = validate("photo.jpg")
result = validate(Path("photo.png"))

# URL (requires: pip install "imageguard[url]")
result = validate("https://example.com/product.jpg")

# Numpy array (RGB, uint8)
arr = np.zeros((480, 640, 3), dtype=np.uint8)
result = validate(arr)

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Use cases

OCR pre-check

from imageguard import validate

result = validate("scan.png", thresholds={"blur_score": 60.0, "resolution_score": 70.0})

if not result.ok:
    raise ValueError(f"Document quality too low for OCR: {result.reason}")

text = ocr_engine.read(scan_path)

Dataset cleaning

from pathlib import Path
from imageguard import validate

accepted, rejected = [], []

for img_path in Path("raw_dataset/").glob("**/*.jpg"):
    result = validate(img_path)
    (accepted if result.ok else rejected).append(img_path)

print(f"Accepted {len(accepted)}, rejected {len(rejected)}")

E-commerce product photo gate

from imageguard import validate

def before_background_removal(image_path: str) -> None:
    result = validate(image_path)
    if result.score < 0.6:
        raise ValueError(
            f"Image quality too low (score {result.score:.2f}): {result.issues}"
        )
    # proceed to AI service…

CI/CD image quality gate (GitHub Actions)

- name: Validate image assets
  run: |
    pip install imageguard
    python -c "
    from pathlib import Path
    from imageguard import validate
    import sys
    failures = [(p, validate(p)) for p in Path('assets/').rglob('*.jpg') if not validate(p).ok]
    if failures:
        for p, r in failures: print(f'FAIL {p.name}: {r.reason} ({r.score:.2f})')
        sys.exit(1)
    "

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Custom thresholds

from imageguard import validate, DEFAULT_THRESHOLDS

print(DEFAULT_THRESHOLDS)
# {'blur_score': 40.0, 'noise_score': 30.0, 'compression_score': 50.0,
#  'pixelation_score': 50.0, 'exposure_score': 40.0,
#  'resolution_score': 60.0, 'overall_score': 40.0}

# Stricter blur check for OCR
result = validate("scan.jpg", thresholds={"blur_score": 60.0})

# More lenient resolution for thumbnails
result = validate("thumb.jpg", thresholds={"resolution_score": 30.0})

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How it works

imageguard computes six quality signals using OpenCV and scikit-image:

Signal	Method
Blur	Laplacian variance + Tenengrad gradient energy, normalised by texture
Noise	SNR + high-pass filter residual on flat regions
Resolution	Pixel count with aspect ratio penalty
Exposure	Histogram balance + entropy + RMS contrast
Compression	8×8 border energy ratio (blockiness)
Pixelation	FFT grid harmonic energy + SSIM round-trip

All signals are normalised to 0–100. The final score (0–1) is a weighted combination with per-issue penalties.

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Dependencies

Package	Purpose
opencv-python	Image loading and signal computation
numpy	Array maths
scikit-image	SSIM for pixelation check
requests (optional)	URL image loading

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Learn more

• Try the online image quality checker — no code needed
• Why AI pipelines fail on bad images
• How to filter blurry images before OCR
• Image validation for machine learning datasets
• Python image quality check guide
• Automate image quality checks in CI/CD

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License

MIT