Craft\ImagerService::_applyWatermark PHP Method

    private function _applyWatermark($imageInstance, $watermark)
    {
        if (!isset($watermark['image'])) {
            throw new Exception(Craft::t('Watermark image property not set'));
        }
        if (!(isset($watermark['width']) && isset($watermark['width']))) {
            throw new Exception(Craft::t('Watermark image size is not set'));
        }
        $paths = new Imager_ImagePathsModel($watermark['image']);
        $watermarkInstance = $this->imagineInstance->open($paths->sourcePath . $paths->sourceFilename);
        $watermarkInstance->resize(new \Imagine\Image\Box($watermark['width'], $watermark['height']), \Imagine\Image\ImageInterface::FILTER_UNDEFINED);
        if (isset($watermark['position'])) {
            $position = $watermark['position'];
            if (isset($position['top'])) {
                $posY = intval($position['top']);
            } else {
                if (isset($position['bottom'])) {
                    $posY = $imageInstance->getSize()->getHeight() - intval($watermark['height']) - intval($position['bottom']);
                } else {
                    $posY = $imageInstance->getSize()->getHeight() - intval($watermark['height']) - 10;
                }
            }
            if (isset($position['left'])) {
                $posX = intval($position['left']);
            } else {
                if (isset($position['right'])) {
                    $posX = $imageInstance->getSize()->getWidth() - intval($watermark['width']) - intval($position['right']);
                } else {
                    $posX = $imageInstance->getSize()->getWidth() - intval($watermark['width']) - 10;
                }
            }
        } else {
            $posY = $imageInstance->getSize()->getHeight() - intval($watermark['height']) - 10;
            $posX = $imageInstance->getSize()->getWidth() - intval($watermark['width']) - 10;
        }
        $positionPoint = new \Imagine\Image\Point($posX, $posY);
        if ($this->imageDriver == 'imagick') {
            $watermarkImagick = $watermarkInstance->getImagick();
            if (isset($watermark['opacity'])) {
                $watermarkImagick->evaluateImage(\Imagick::EVALUATE_MULTIPLY, floatval($watermark['opacity']), \Imagick::CHANNEL_ALPHA);
            }
            if (isset($watermark['blendMode']) && isset(ImagerService::$compositeKeyTranslate[$watermark['blendMode']])) {
                $blendMode = ImagerService::$compositeKeyTranslate[$watermark['blendMode']];
            } else {
                $blendMode = \Imagick::COMPOSITE_ATOP;
            }
            $imageInstance->getImagick()->compositeImage($watermarkImagick, $blendMode, $positionPoint->getX(), $positionPoint->getY());
        } else {
            // it's GD :(
            $imageInstance->paste($watermarkInstance, $positionPoint);
        }
    }