随机字符串生成图片 PHP代码

<?php

/*
作用：取得随机字符串
参数：
1、(int)$length = 32 #随机字符长度，默认为32
2、(int)$mode = 0 #随机字符类型，0为大小写英文和数字，1为数字，2为小写子木，3为大写字母，4为大小写字母，5为大写字母和数字，6为小写字母和数字
返回：取得的字符串
*/
function getCode ($length = 32, $mode = 0)
{
switch ($mode) {
case "1":
$str = "1234567890";
break;
case "2":
$str = "abcdefghijklmnopqrstuvwxyz";
break;
case "3":
$str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
break;
case "4":
$str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
break;
case "5":
$str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
break;
case "6":
$str = "abcdefghijklmnopqrstuvwxyz1234567890";
break;
default:
$str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890";
break;
}
$result="";
$l=strlen($str);
for($i=0;$i < $length;$i++){
$num = rand(0, $l-1); //如果$i不减1,将不一定生成4位数, 因为$num = rand(0,10).会随机产生10,$str[10] 为空
$result .= $str[$num];
}
return $result;
}

$authnum =getCode(4,1);

//生成验证码图片
Header("Content-type: image/JPEG");
//srand((double)microtime()*1000000);
//建立空白图片
$im = imagecreate(50,20);
//为图片分配颜色
//黑色
$black = ImageColorAllocate($im, 0,0,0);
//白色
$white = ImageColorAllocate($im, 255,255,255);
//灰色
$gray = ImageColorAllocate($im, 200,200,200);
//将四位整数验证码绘入图片
//ImageTTFText($im,16,0,5,18,$white,"simhei.ttf",$authnum);
imagestring($im, 5, 6, 3, $authnum, $white);
//加入干扰象素
for($i=0;$i<200;$i++)
{
imagesetpixel($im, rand()%70, rand()%30, $gray);
}
ImageJPEG($im);
ImageDestroy($im);

?>