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                        /PHP實現(xiàn)驗證碼制作

一直都是提示輸入錯誤

輸入驗證碼一直都是顯示輸入錯誤，兩個頁面都有?session_start();? 大神救命~~

#form.php

<?php
error_reporting(E_ALL & ~E_NOTICE);
header("Content-type:text/html;charset=utf-8");
?if(isset($_REQUEST['authcode'])){
??session_start();
??
?if(strtolower($_REQUEST['authcode'])==$_SESSION['authcode']){
??echo'<font color="#0000CC">輸入正確</font>';??
?}else{
??echo'<font color="#CC0000"><b>輸入錯誤</b></font>';?
?}
?exit();
?}
?>

<!DOCTYPE html>
<html>
?<head>
??<meta charset="utf-8"/>
??<title>確認驗證碼</title>
?</head>
?<body>
??<form method="post" action="./form.php">
???<p>驗證證圖片:<img border="1" src="./captcha.php?r=<?php echo rand();?>"border="1" width="100px" height="30px"/></p>
?
???<p>請輸入圖片中的內容:<input type="text" name="authcode" value=""/></p>
?<p><input type="submit" value="提交" style="padding:6px 20px;"></p>
?</form>?
?</body>

</html>

#captcha.php

<?php

??? session_start();
?
?
?$image = imagecreatetruecolor(100,30);
?$bgcolor=imagecolorallocate($image,255,255,255);//ffffff
?imagefill($image,0,0,$bgcolor);
?
?
?/*for($i=0;$i<4;$i++){
??$fontsize=6;
??$fontcolor=imagecolorallocate($image,rand(0,120),rand(0,120),rand(0,120));
??$fontcontent=rand(0,9);
?
??$x=($i*100/4)+rand(5,10);
??$y=rand(5,10);
??
??imagestring($image,$fontsize,$x,$y,$fontcontent,$fontcolor);
?}*/
?$captch_code='';
?
?for($i=0;$i<4;$i++){
??$fontsize=6;
??$fontcolor=imagecolorallocate($image,rand(0,120),rand(0,120),rand(0,120));
??
??$data='abcdefgfijklmnopqrstuvwxyz0123456789';
??$fontcontent=substr($data,rand(0,strlen($data)),1);
??$captch_code.=$fontcontent;
??
??$x=($i*100/4)+rand(5,10);
??$y=rand(5,10);
??
??imagestring($image,$fontsize,$x,$y,$fontcontent,$fontcolor);
?}
?$SESSION['authcode']=$captch_code;
?
?
?for($i=0;$i<200;$i++){
??$pointcolor=imagecolorallocate($image,rand(50,200),rand(50,200),rand(5,200));
??imagesetpixel($image,rand(1,99),rand(1,29),$pointcolor);?
?}
?for($i=0;$i<3;$i++){
??$linecolor=imagecolorallocate($image,rand(80,220),rand(80,220),rand(80,220));
??imageline($image,rand(1,99),rand(1,29),rand(1,99),rand(1,29),$linecolor);
?}
?
?
?header('content-type:image/png');
?imagepng( $image );