Add watermark to image using PHP

A guide on how to add a watermark to an image using PHP with the GD library. This PHP script allows adding text or image watermark on top of the original image.

<?php
function addWatermark($source_image_path, $watermark_image_path, $output_image_path, $position = 'bottom-right', $opacity = 50) {
    // Get original image info
    list($source_width, $source_height, $source_type) = getimagesize($source_image_path);
    
    // Create image from source file
    switch ($source_type) {
        case IMAGETYPE_JPEG:
            $source_image = imagecreatefromjpeg($source_image_path);
            break;
        case IMAGETYPE_PNG:
            $source_image = imagecreatefrompng($source_image_path);
            break;
        case IMAGETYPE_GIF:
            $source_image = imagecreatefromgif($source_image_path);
            break;
        default:
            return false;
    }

    // Create watermark image from file
    list($watermark_width, $watermark_height) = getimagesize($watermark_image_path);
    $watermark_image = imagecreatefrompng($watermark_image_path);
    imagealphablending($watermark_image, true);
    
    // Determine watermark position
    switch ($position) {
        case 'top-left':
            $x = 0;
            $y = 0;
            break;
        case 'top-right':
            $x = $source_width - $watermark_width;
            $y = 0;
            break;
        case 'bottom-left':
            $x = 0;
            $y = $source_height - $watermark_height;
            break;
        case 'bottom-right':
        default:
            $x = $source_width - $watermark_width;
            $y = $source_height - $watermark_height;
            break;
    }

    // Add watermark to original image
    imagecopymerge($source_image, $watermark_image, $x, $y, 0, 0, $watermark_width, $watermark_height, $opacity);

    // Save the new image
    switch ($source_type) {
        case IMAGETYPE_JPEG:
            imagejpeg($source_image, $output_image_path, 90);
            break;
        case IMAGETYPE_PNG:
            imagepng($source_image, $output_image_path);
            break;
        case IMAGETYPE_GIF:
            imagegif($source_image, $output_image_path);
            break;
    }

    // Free memory
    imagedestroy($source_image);
    imagedestroy($watermark_image);

    return true;
}

// Use the function
$source_image = 'source_image.jpg';
$watermark_image = 'watermark.png';
$output_image = 'watermarked_image.jpg';

if (addWatermark($source_image, $watermark_image, $output_image)) {
    echo "Watermark added successfully!";
} else {
    echo "Failed to add watermark.";
}
?>

Detailed explanation:

  1. Get original image info:

    • getimagesize($source_image_path): Retrieves the dimensions and type of the original image.

  2. Create image from source file:

    • Use imagecreatefromjpeg, imagecreatefrompng, imagecreatefromgif to generate an image resource based on the original image format.

  3. Create watermark image:

    • imagecreatefrompng($watermark_image_path): Creates the watermark image from a PNG file, which supports transparency.

  4. Determine watermark position:

    • The options top-left, top-right, bottom-left, bottom-right allow specifying where to position the watermark on the original image.

  5. Add watermark to original image:

    • imagecopymerge(): Blends the watermark into the original image at the specified position with the given transparency level (opacity).

  6. Save the new image:

    • Saves the modified image in its original format using imagegif, imagejpeg, or imagepng.

  7. Free memory:

    • imagedestroy(): Frees memory used by the images to prevent memory overload.

  8. Use the function:

    • Executes the watermarking process, saving the final image as a new file.

PHP Version:

This code runs on PHP 5.0 and above, with the GD extension required for image processing.

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