image with text water mark PHP

<?php

function getx($img, $font, $text) {
    $image_width = imagesx($img);
    $string_width = imagefontwidth($font) * strlen($text);
    return $string_x_position = ($image_width - $string_width) / 2;
}

function gety($img, $font, $text) {
    $image_height = imagesy($img);
    $string_height = imagefontheight($font);
    return $string_y_position = ($image_height - $string_height) / 2;
}

function watermark($input_image, $output_image) {

    list($width, $height) = getimagesize($input_image);
    $imageProperties = imagecreatetruecolor($width, $height);
    
    // get input file extension
    $ext = pathinfo($input_image, PATHINFO_EXTENSION);
    if($ext == 'png'){
        $targetLayer = imagecreatefrompng($input_image);
    }
    if($ext == 'jpg' || $ext == 'jpeg'){
        $targetLayer = imagecreatefromjpeg($input_image);
    }
    if($ext == 'gif'){
        $targetLayer = imagecreatefromgif($input_image);
    }
    
    imagecopyresampled($imageProperties, $targetLayer, 0, 0, 0, 0, $width, $height, $width, $height);

    $WaterMarkText = 'CONFIDENTIAL';
    $watermarkColor = imagecolorallocate($imageProperties, 255, 255, 255); // Font Color

    $font = 10;
    $xpos = getx($targetLayer, $font, $WaterMarkText);
    $ypos = gety($targetLayer, $font, $WaterMarkText);

    imagestring($imageProperties, 5, $xpos, $ypos, $WaterMarkText, $watermarkColor);
        
    header('Content-type: image/jpeg');
    
    // Save the image as $output_image
    imagejpeg($imageProperties, $output_image);

    imagepng($imageProperties);
    imagedestroy($targetLayer);
    imagedestroy($imageProperties);
}

$input_image = "./input.png"; // Input File 
$output_image = "./output.jpg"; // Output File
watermark($input_image, $output_image);