PHP编写登录验证码功能 附调用方法

<?php
session_start();
//设置cookie或session
function esetcookie($name,$str,$life=0){
//本函数将字符串 str 全部变小写字符串使验证码输入不区分大小写----在提交表单进行session比较同样需要次函数转化
 $_session[$name]=strtolower($str);
}

//获取随机字符 此函数区分字符大小写 如果不区分大小写可加入函数strtolower
function domake_password($len) 
{ 
  $chars = array( 
    /*"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", 
    "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", 
    "w", "x", "y", "z", "a", "b", "c", "d", "e", "f", "g", 
    "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", 
    "s", "t", "u", "v", "w", "x", "y", "z",*/ "0", "1", "2", 
    "3", "4", "5", "6", "7", "8", "9" 
  ); 
  $charslen = count($chars) - 1; 
  shuffle($chars);// 将数组打乱
  $output = ""; 
  for ($i=0; $i<$len; $i++) 
  { 
    $output .= $chars[mt_rand(0, $charslen)]; //获得一个数组元素
  } 
  return $output;
} 

//显示验证码
function showkey(){
 $key=domake_password(4);//获取随机值
 $set=esetcookie("checkkey",$key);//将随机值写入cookie或session
 //是否支持gd库
 if(function_exists("imagejpeg")) 
 {
  header ("content-type: image/jpeg");
  $img=imagecreate(47,20);
  $blue=imagecolorallocate($img,102,102,102);
  $white=imagecolorallocate($img,255,255,255);
  $black=imagecolorallocate($img,71,71,71);
  imagefill($img,0,0,$blue);
  imagestring($img,5,6,3,$key,$white);
  for($i=0;$i<90;$i++) //加入干扰象素
  {
   imagesetpixel($img,rand()%70,rand()%30,$black);
  }
  imagejpeg($img);
  imagedestroy($img);
 }
 elseif (function_exists("imagepng"))
 {
  header ("content-type: image/png");
  $img=imagecreate(47,20);
  $blue=imagecolorallocate($img,102,102,102);
  $white=imagecolorallocate($img,255,255,255);
  $black=imagecolorallocate($img,71,71,71);
  imagefill($img,0,0,$blue);
  imagestring($img,5,6,3,$key,$white);
  for($i=0;$i<90;$i++) //加入干扰象素
  {
   imagesetpixel($img,rand()%70,rand()%30,$black);
  }
  imagepng($img);
  imagedestroy($img);
 }
 elseif (function_exists("imagegif")) 
 {
  header("content-type: image/gif");
  $img=imagecreate(47,20);
  $blue=imagecolorallocate($img,102,102,102);
  $white=imagecolorallocate($img,255,255,255);
  $black=imagecolorallocate($img,71,71,71);
  imagefill($img,0,0,$blue);
  imagestring($img,5,6,3,$key,$white);
  for($i=0;$i<90;$i++) //加入干扰象素
  {
   imagesetpixel($img,rand()%70,rand()%30,$black);
  }
  imagegif($img);
  imagedestroy($img);
 }
 elseif (function_exists("imagewbmp")) 
 {
  header ("content-type: image/vnd.wap.wbmp");
  $img=imagecreate(47,20);
  $blue=imagecolorallocate($img,102,102,102);
  $white=imagecolorallocate($img,255,255,255);
  $black=imagecolorallocate($img,71,71,71);
  imagefill($img,0,0,$blue);
  imagestring($img,5,6,3,$key,$white);
  for($i=0;$i<90;$i++) //加入干扰象素
  {
   imagesetpixel($img,rand()%70,rand()%30,$black);
  }
  imagewbmp($img);
  imagedestroy($img);
 }
 else
 {
  //不支持验证码
  header("content-type:image/jpeg\r\n");
  header("pragma:no-cache\r\n");
  header("cache-control:no-cache\r\n");
  header("expires:0\r\n");
  $fp = fopen("data/vdcode.jpg","r"); 
 }
}
showkey();
?>