PHP: Add watermark to image

add_watermark.php

/**
 * Create JPEG image with watermark.
 * @param string $sourceImage path to source JPEG image
 * @param string $watermark path to watermark in GIF format
 * @param string $targetImage path to final JPEG image file
 * @param int $transparency watermark transparency (0 transparent - 100 solid)
 * @param int $quality quality of final image (0-100)
 * @param int offsetX offset of watermark from edge in horizontal direction
 * @param int $offsetY offset of watermark from edge in vertical direction
 * @param string $alignX alignment of watermark in horizontal direction (left, middle, right)
 * @param string $alignY allignment of watermark in vertical direction (top, middle, bottom)
 * @return bool
 */
function addWatermark($sourceImage, $watermark, $targetImage, $transparency = 100, $quality = 80, $offsetX = 10, $offsetY = 10, $alignX = 'right', $alignY = 'bottom')
{
    // Obtain image from given source file.
    if (!$image = @imagecreatefromjpeg($sourceImage))
    {
        return false;
    }

    if (!$imageWatermark = @imagecreatefromgif($watermark))
    {
        return false;
    }

    // Get dimensions of source image.
    list($imageWidth, $imageHeight) = getimagesize($sourceImage);

    // Get dimensions of watermark.
    list($watermarkWidth, $watermarkHeight) = getimagesize($watermark);

    // Supported horizontal and vertical alignments.
    $alignmentsX = array('left', 'middle', 'right');
    $alignmentsY = array('top', 'middle', 'bottom');

    // Set default horizontal and vertical alignments if the parameters are incorrect.
    if (!in_array($alignX, $alignmentsX))
    {
        $alignX = 'right';
    }
    
    if (!in_array($alignY, $alignmentsY))
    {
        $alignY = 'bottom';
    }

    // Calculate horizontal position of watermark.
    if ($alignX == 'middle')
    {
        $posX = $imageWidth/2 - $watermarkWidth/2 + $offsetX;
    }
    elseif ($alignX == 'left')
    {
        $posX = $offsetX;
    }
    elseif ($alignX == 'right')
    {
        $posX = $imageWidth - $watermarkWidth - $offsetX;
    }

    // Calculate vertical position of watermark.
    if ($alignY == 'middle')
    {
        $posY = $imageHeight/2 - $watermarkHeight/2 + $offsetY;
    }
    elseif ($alignY == 'top')
    {
        $posY = $offsetY;
    }
    elseif ($alignY == 'bottom')
    {
        $posY = $imageHeight - $watermarkHeight - $offsetY;
    }

    // Add watermark to the image.
    imagecopymerge($image, $imageWatermark, $posX, $posY, 0, 0, $watermarkWidth, $watermarkHeight, $transparency);

    // Create final image.
    imagejpeg($image, $targetImage, $quality);

    // Free up the memory.
    imagedestroy($image);
    imagedestroy($imageWatermark);

    return true;
}

/**
 * Example:
 * addWatermark('image.jpg', 'watermark.gif', 'final.jpg');
 */