Image Watermarking

Add visible and invisible watermarks to protect images.

Overview

Add watermarks for copyright protection. Includes visible text/logo watermarks and invisible steganographic watermarks.

Key Techniques:

Image blending (addWeighted)
Alpha channel manipulation
Bitwise operations
LSB steganography

Watermark Types

1. Text Watermark

def text_watermark(image, text, position, opacity=0.5):
    overlay = image.copy()
    font = cv2.FONT_HERSHEY_SIMPLEX

    cv2.putText(overlay, text, position, font, 1.0, (255, 255, 255), 2)

    # Blend original and overlay
    result = cv2.addWeighted(overlay, opacity, image, 1 - opacity, 0)
    return result

2. Logo Watermark

def logo_watermark(image, logo, position, opacity=0.3):
    # Resize logo
    logo_resized = cv2.resize(logo, (100, 100))

    # Extract ROI
    x, y = position
    h, w = logo_resized.shape[:2]
    roi = image[y:y+h, x:x+w]

    # Blend
    blended = cv2.addWeighted(logo_resized, opacity, roi, 1 - opacity, 0)
    image[y:y+h, x:x+w] = blended

    return image

3. Tiled Watermark

def tiled_watermark(image, text, spacing=150, opacity=0.1):
    overlay = np.zeros_like(image)

    for y in range(0, image.shape[0], spacing):
        for x in range(0, image.shape[1], spacing):
            cv2.putText(overlay, text, (x, y),
                       cv2.FONT_HERSHEY_SIMPLEX, 0.8, (200, 200, 200), 2)

    return cv2.addWeighted(overlay, opacity, image, 1, 0)

Invisible Watermark (LSB)

Hide data in the least significant bits of pixels:

def embed_watermark(image, text):
    result = image.copy()
    binary = ''.join(format(ord(c), '08b') for c in text)
    binary += '00000000'  # Null terminator

    flat = result[:, :, 0].flatten()

    for i, bit in enumerate(binary):
        if i >= len(flat):
            break
        flat[i] = (flat[i] & 0xFE) | int(bit)  # Replace LSB

    result[:, :, 0] = flat.reshape(result[:, :, 0].shape)
    return result

def extract_watermark(image):
    flat = image[:, :, 0].flatten()
    bits = ''.join(str(flat[i] & 1) for i in range(1000))

    text = ''
    for i in range(0, len(bits), 8):
        byte = bits[i:i+8]
        if byte == '00000000':
            break
        text += chr(int(byte, 2))

    return text

Controls

Key	Action
`1`	Text watermark
`2`	Logo watermark
`3`	Tiled watermark
`4`	Invisible watermark
`5`	Extract invisible watermark
`p`	Change position
`+/-`	Adjust opacity
`s`	Save result
`q`	Quit

Running the Application

python curriculum/applications/09_image_watermark.py