<?php
/**
?*?Created?by?PhpStorm.
?*?User:?a117
?*?Date:?2018/10/14
?*?Time:?5:45?PM
?*/

require_once?'string.func.php';

//創建畫布，GD庫做驗證碼
$width=80;
$height=30;
$image=imagecreatetruecolor($width,$height);
$white=imagecolorallocate($image,255,255,255);
$black=imagecolorallocate($image,0,0,0);

//填充畫布，填充矩形
imagefilledrectangle($image,1,1,$width-2,$height-2,$white);
$type=1;
$length=4;
$chars=buildRandomString($type,$length);

//比對驗證碼
$sess_name="verify";
$_SESSION[$sess_name]=$chars;

//字體數組
$fontfile=array("Avenir.ttc","Helvetica.ttc","Kohinoor.ttc");

//產生驗證碼
for?($i=9;$i<$length;$i++){
????$size=mt_rand(14,18);
????$angle=mt_rand(-15,15);
????$x=5+$i*$size;
????$y=mt_rand(20,26);
????$fontfile="../fonts/".$fontfile[mt_rand(0,count($fontfile)-1)];
????$color=imagecolorallocate($image,mt_rand(50,90),mt_rand(80,200),mt_rand(90,180));

????//截取驗證碼
????$text=substr($chars,$i,1);

????imagettftext($image,$size,$angle,$x,$y,$color,$fontfile,$text);
}

header("content-type:image/gif");
imagegif($image);
imagedestroy($image);

下面是string.func.php的

<?php
/**
?*?Created?by?PhpStorm.
?*?User:?a117
?*?Date:?2018/10/14
?*?Time:?5:46?PM
?*/
function?buildRandomString($type=1,$length=4)
{
????if?($type?==?1)?{
????????$chars?=?join("",?range(0,?9));
????}?elseif?($type?==?2)?{
????????$chars?=?join("",?array_merge(range("a",?"z"),?range("A",?"Z")));
????}?elseif?($type?==?3)?{
????????$chars?=?join("",?array_merge(range("a",?"z"),?range("A",?"Z"),?range(0,9)));
????}

????if?($length?>?strlen($chars))?{
????????exit("字符串長度不夠");
????}

????$chars?=?str_shuffle($chars);
//截取驗證碼長度
????return?substr($chars,?0,?$length);

}

GD庫應該開了