Principle of watermarking pictures in PHP (super simple example code)_PHP tutorial

$w = 80;
$h = 20;
$im = imagecreatetruecolor($w,$h);
$textcolor = imagecolorallocate($im, 123, 12, 255);
$white = imagecolorallocate($im, 255, 255, 255);
$grey = imagecolorallocate($im, 128, 128, 128);
$black = imagecolorallocate($im, 0, 0, 0);
imagefilledrectangle($im, 0, 0, 399, 29 , $grey); //Draw a rectangle and fill it

// Write the string in the upper left corner of the image
imagestring($im, 3, 2, 3, "Hello world!", $textcolor );

// Output image
header("Content-type: image/jpeg");
imagejpeg($im);
imagedestroy($im);

Image watermark

$groundImg = "DSC05940.jpeg";
$groundInfo = getimagesize($groundImg);
$ground_w = $groundInfo[0];
//print_r( $groundInfo);
$ground_h = $groundInfo[1];
switch($groundInfo[2]){
case 1:
$ground_im = imagecreatefromgif($groundImg);
break ;
case 2:
$ground_im = imagecreatefromjpeg($groundImg);
break;
case 3:
$ground_im = imagecreatefrompng($groundImg);
break;
}

$waterImg = "DSC05949.jpeg";
$imgInfo =getimagesize($waterImg);
$water_w = $imgInfo[0];
$water_w = $imgInfo[1 ];

switch($imgInfo[2]){
case 1:
$water_im = imagecreatefromgif($waterImg);
break;
case 2:
$ water_im = imagecreatefromjpeg($waterImg);
break;
case 3:
$water_im = imagecreatefrompng($waterImg);
break;
}
imagecopy($ground_im,$water_im ,100,100,0,0,500,500);
header("Content-type: image/jpeg");

imagejpeg($ground_im);