PHP生成图形验证码（大小写字母与数字混合）

1. header("content-type:image/png");
2. $num = $_GET['num'];
3. $imagewidth=60;
4. $imageheight=18;
5. srand(microtime() * 100000);
7. $numimage = imagecreate($imagewidth,$imageheight);
8. imagecolorallocate($numimage,183,180,83);
9. for($i=0;$i $font = mt_rand(3,5);
10. $x = mt_rand(1,8)+$imagewidth*$i/4;
11. $y = mt_rand(1,$imageheight/3);
12. $color=imagecolorallocate($numimage,mt_rand(0,50),mt_rand(0,150),mt_rand(0,255));
13. imagestring($numimage,$font,$x,$y,$num[$i],$color);
14. }
15. imagepng($numimage);
16. imagedestroy($numimage);
17. ?>
21. 调用方法：
22. session_start();
23. include_once 'conn/conn.php';
24. $pattern = '1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLOMNOPQRSTUVWXYZ';
25. $num = null;
26. for($i = 0; $i $num .= $pattern{mt_rand(0, 61)};
27. }
28. ?>
30. 验证码：
32. 

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验证码, 写字母, PHP