PHP development verification code using session to store verification information

<?php
session_start();
$image = imagecreatetruecolor(100,30);
$bgcolor = imagecolorallocate($image,255,255,255);//#FFFFFFFFFFFF
imagefill($image,0,0,$bgcolor);
$captch_code="";
for ($i=0;$i<4;$i++){
    $fontsize = 6;
    $fontcolor = imagecolorallocate($image,rand(0,120),rand(0,120),rand(0,120));
    $data='abcdefghijklmnopqrstuvwxyz1234567890';
    $fontcontent=substr($data,rand(0,strlen($data)),1);
    $captch_code.="$fontcontent";
    $x = ($i * 100/4)+rand(5,10);
    $y = rand(5,10);
    imagestring($image,$fontsize,$x,$y,$fontcontent,$fontcolor);
}
$_SESSION['code']=$captch_code;
for($i=0;$i<200;$i++){
    $pointcolor = imagecolorallocate($image,rand(50,200),rand(50,200),rand(50,200));
    imagesetpixel($image,rand(1,99),rand(1,29),$pointcolor);
}
for($i=0;$i<8;$i++){
    $linecolor = imagecolorallocate($image,rand(60,220),rand(60,220),rand(60,220));
    imageline($image,rand(1,99),rand(1,29),rand(1,99),rand(1,29),$linecolor);
}
header('content-type: image/png');
imagepng($image);
//销毁
imagedestroy($image);
?>

$_SESSION['code']=$captch_code; is placed after the generated verification code. Each time the verification code is generated, the value will be obtained and stored in the code.

Use session_start() to store verification Code

Note that session_start() must be at the top of the script