下面是php生成验证码的源码：
<p><?php<br /></p>session_start();<br />//session_register('CheckCode'); <br />//PHP4.2以上版本不需要用session_register()注册SESSION变量<br />$type='gif';<br />$width= 45;<br />$height= 20;<br />header("Content-type: image/".$type);<br />srand((double)microtime()*1000000);<br />if(isset($_GET['action'])){<br /> $randval=randStr(4,$_GET['action']); <br />}else{<br /> $randval=randStr(4,''); <br />}<br />if($type!='gif'&&function_exists('imagecreatetruecolor')){<br /> $im=@imagecreatetruecolor($width,$height);<br />}else{<br /> $im=@imagecreate($width,$height);<br />}<br />$r=Array(225,211,255,223);<br />$g=Array(225,236,237,215);<br />$b=Array(225,236,166,125);<br />$key=rand(0,3);<br />$backColor=ImageColorAllocate($im,$r[$key],$g[$key],$b[$key]);//背景色（随机）<br />$borderColor=ImageColorAllocate($im,127,157,185);//边框色<br />$pointColor=ImageColorAllocate($im,255,170,255);//点颜色<br />@imagefilledrectangle($im,0,0,$width - 1,$height - 1,$backColor);//背景位置<br />@imagerectangle($im,0,0,$width-1,$height-1,$borderColor); //边框位置<br />$stringColor=ImageColorAllocate($im,255,51,153);<br />for($i=0;$i<=100;$i++){<br /> $pointX=rand(2,$width-2);<br /> $pointY=rand(2,$height-2);<br /> @imagesetpixel($im,$pointX,$pointY,$pointColor);<br />}<br />@imagestring($im,5,5,1,$randval,$stringColor);<br />$ImageFun='Image'.$type;<br />$ImageFun($im);<br />@imagedestroy($im);<br />$_SESSION['CheckCode']=$randval;<br />function randStr($len=6,$format='ALL'){<br /> switch($format){<br /> case 'ALL'://生成包含数字和字母的验证码<br /> $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'; break;<br /> case 'CHAR'://仅生成包含字母的验证码<br /> $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'; break;<br /> case 'NUMBER'://仅生成包含数字的验证码<br /> $chars='0123456789'; break;<br /> default :<br /> $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'; break;<br /> }<br /> $string='';<br /> while(strlen($string)<$len)<br /> $string.=substr($chars,(mt_rand()%strlen($chars)),1);<br /> return $string;<br /><p>}</p>该函数的具体使用方法请看如下这个示例（这里是生成全数字的验证码）：
<img src="checkCode.php?action=NUMBER" style="max-width:90%" style="max-width:90%" / alt="php生成验证码函数" >
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