How to overlay one image on another in php?

Question

PHP

The essence is this:
I need to overlay one image (.jpg) on ​​another (.png).
The output should be .png, since .jpg will be inside.
I do this, the output is .jpg:

<?php
$file_dir = $_POST['file_dir'];
$file_width = $_POST['file_width'];
$file_height = $_POST['file_height'];
$file_posX = $_POST['file_posX'];
$file_posY = $_POST['file_posY'];
$file_bckg = $_POST['file_bckg'];

$path = $_SERVER['DOCUMENT_ROOT'];
$imgBig = '/ajax/dist/square.png';
if($file_bckg == 'circle'):
$imgBig = '/ajax/dist/circle.png';
endif;
$imgSmall = $file_dir;

/* ------------------------ */

list($width, $height) = getimagesize($path.$file_dir);

$thumb = imagecreatetruecolor($file_width, $file_height);
$source = imagecreatefromjpeg($path.$file_dir);
imagecopyresized($thumb, $source, 0, 0, 0, 0, $file_width, $file_height, $width, $height);
$target = '/ajax/resize_img/'.date("d_m_Y_H_i_s")."_".rand(0,1000).".jpg";
imagejpeg($thumb, $path.$target, 100);
$img_resize = $target;
unset($target);
/* ------------------------ */

$img1 = imagecreatefrompng($path . $imgBig);
$img2 = imagecreatefromjpeg($path . $img_resize);

if($img1 and $img2) {	
    $x2 = imagesx($img2);
    $y2 = imagesy($img2);
    imagecopyresampled($img1,$img2,$file_posX,$file_posY,0,0,$x2,$y2,$x2,$y2);
  $target = '/ajax/save_img/'.date("d_m_Y_H_i_s")."_".rand(0,1000).".jpg";
    imagejpeg($img1, $path.$target, 100);

  echo $target;
  
} else {
    header('HTTP/1.1 404 Not Found');
}
?>

And one more problem, when overlaying, a part of .png is overwritten:

Original:

Answer 1

Try the image.intervention.io library for image manipulation, it will be easier and clearer.
It can be assumed that the lost part on the png image had transparency and after merging it got a black background. Check this section of the original in a graphical editor.