PHP實(shí)戰(zhàn)
<?php
    session_start ();
    header ( 'Content-type: image/png' );
    //創(chuàng)建圖片
    $im = imagecreate($x=130,$y=45 );
    $bg = imagecolorallocate($im,rand(50,200),rand(0,155),rand(0,155)); //第一次對(duì) imagecolorallocate() 的調(diào)用會(huì)給基于調(diào)色板的圖像填充背景色
    $fontColor = imageColorAllocate ( $im, 255, 255, 255 );  //字體顏色
    $fontstyle = 'rock.ttf';          //字體樣式,這個(gè)可以從c:windowsFonts文件夾下找到,我把它放到和authcode.php文件同一個(gè)目錄,這里可以替換其他的字體樣式
    //產(chǎn)生隨機(jī)字符
    for($i = 0; $i < 4; $i ++) {
        $randAsciiNumArray     = array (rand(48,57),rand(65,90));
        $randAsciiNum         = $randAsciiNumArray [rand ( 0, 1 )];
        $randStr             = chr ( $randAsciiNum );
        imagettftext($im,30,rand(0,20)-rand(0,25),5+$i*30,rand(30,35),$fontColor,$fontstyle,$randStr);
        $authcode            .= $randStr;
    }
    $_SESSION['authcode']    = $randFourStr;//用戶和用戶輸入的驗(yàn)證碼做比較
    //干擾線
    for ($i=0;$i<8;$i++){
        $lineColor    = imagecolorallocate($im,rand(0,255),rand(0,255),rand(0,255));
        imageline ($im,rand(0,$x),0,rand(0,$x),$y,$lineColor);
    }
    //干擾點(diǎn)
    for ($i=0;$i<250;$i++){
        imagesetpixel($im,rand(0,$x),rand(0,$y),$fontColor);
    }
    imagepng($im);
    imagedestroy($im);
?>

PHP實(shí)戰(zhàn)
//首先開啟session
session_start();
//定義前臺(tái)顯示驗(yàn)證碼長(zhǎng)&寬
$image_width = 120;
$image_height = 40;
$characters_on_image = 6;
$font = './monofont.ttf';
//The characters that can be used in the CAPTCHA code.
//avoid confusing characters (l 1 and i for example)
$possible_letters = '23456789bcdfghjkmnpqrstvwxyz';
$random_dots = 10;
$random_lines = 30;
$captcha_text_color="0x142864";
$captcha_noice_color = "0x142864";
//定義要生成驗(yàn)證碼的字符串
$code = '';
$i = 0;
while ($i < $characters_on_image) {
$code .= substr($possible_letters, mt_rand(0, strlen($possible_letters)-1), 1);
$i++;
}
$font_size = $image_height * 0.75;
$image = @imagecreate($image_width, $image_height);
/* setting the background, text and noise colours here */
$background_color = imagecolorallocate($image, 255, 255, 255);
$arr_text_color = hexrgb($captcha_text_color);
$text_color = imagecolorallocate($image, $arr_text_color['red'],
    $arr_text_color['green'], $arr_text_color['blue']);
$arr_noice_color = hexrgb($captcha_noice_color);
$image_noise_color = imagecolorallocate($image, $arr_noice_color['red'],
    $arr_noice_color['green'], $arr_noice_color['blue']);
/* generating the dots randomly in background */
for( $i=0; $i<$random_dots; $i++ ) {
imagefilledellipse($image, mt_rand(0,$image_width),
 mt_rand(0,$image_height), 2, 3, $image_noise_color);
}
/* generating lines randomly in background of image */
for( $i=0; $i<$random_lines; $i++ ) {
imageline($image, mt_rand(0,$image_width), mt_rand(0,$image_height),
 mt_rand(0,$image_width), mt_rand(0,$image_height), $image_noise_color);
}
/* create a text box and add 6 letters code in it */
$textbox = imagettfbbox($font_size, 0, $font, $code);
$x = ($image_width - $textbox[4])/2;
$y = ($image_height - $textbox[5])/2;
imagettftext($image, $font_size, 0, $x, $y, $text_color, $font , $code);
/* Show captcha image in the page html page */
header('Content-Type: image/jpeg');// defining the image type to be shown in browser widow
imagejpeg($image);//showing the image
imagedestroy($image);//destroying the image instance
//設(shè)置session,做驗(yàn)證
$_SESSION['6_letters_code'] = $code;
function hexrgb ($hexstr)
{
 $int = hexdec($hexstr);
 return array("red" => 0xFF & ($int >> 0x10),
        "green" => 0xFF & ($int >> 0x8),
        "blue" => 0xFF & $int);
}

PHP實(shí)戰(zhàn)
<?php
session_start();
if(isset($_REQUEST['Submit'])){
  // code for check server side validation
  if(emptyempty($_SESSION['6_letters_code'] ) ||
    strcasecmp($_SESSION['6_letters_code'], $_POST['6_letters_code']) != 0)
  {
    $msg="您輸入的驗(yàn)證碼有誤,請(qǐng)重新輸入!";
  }else{
    echo "您輸入的是正確的!";
    // Captcha verification is Correct. Final Code Execute here!
  }
}
?>
<style type="text/css">
.table{
  font-family:Arial, Helvetica, sans-serif;
  font-size:12px;
  color:#333;
  background-color:#E4E4E4;
}
.table td{
  background-color:#F8F8F8;
}
</style>
<form action="" method="post" name="form1" id="form1" >
 <table width="400" border="0" align="center" cellpadding="5" cellspacing="1">
<?php if(isset($msg)){?>
  <tr>
   <td colspan="2" align="center" valign="top"><?php echo $msg;?></td>
  </tr>
<?php } ?>
  <tr>
   <td align="right" valign="top"> 驗(yàn)證碼Demo:</td>
   <td><img src="captcha_code_file.php?rand=<?php echo rand(0,20);?>" id='captchaimg' onclick="refreshCaptcha();" ><br>
    <label for='message'>請(qǐng)輸入驗(yàn)證碼:</label>
    <br>
    <input id="6_letters_code" name="6_letters_code" type="text">
    <br>
    如果看不到,請(qǐng) <a href='javascript： refreshCaptcha();'>點(diǎn)我</a> 刷新一下!
    </p></td>
  </tr>
  <tr>
   <td>&nbsp;</td>
   <td><input name="Submit" type="submit" onclick="return validate();" value="Submit"></td>
  </tr>
 </table>
</form>
<script type='text/javascript'>
//定義的刷新請(qǐng)求
function refreshCaptcha()
{
  var img = document.images['captchaimg'];
  img.src = img.src.substring(0,img.src.lastIndexOf("?"))+"?rand="+Math.random()*1000;
}
</script>

PHP實(shí)戰(zhàn)
<?session_start();?>
<FORM METHOD=POST ACTION="">
<input type=text name=number maxlength=4><img src="YanZhengMa.php?act=init">
<INPUT TYPE="submit" name="sub">
</FORM>
<?
//檢驗(yàn)校驗(yàn)碼
if(isset($HTTP_POST_VARS["sub"])):
if($HTTP_POST_VARS["number"] != $HTTP_SESSION_VARS[login_check_number] || emptyempty($HTTP_POST_VARS["number"])){
  echo "校驗(yàn)碼不正確!" ;
}else{
  echo"驗(yàn)證碼通過!";
}
endif;
show_source('test.php');
//以上本頁(yè)的源碼
//以下是生成驗(yàn)證碼的源碼
show_source('YanZhengMa.php');
?>
<?php
session_start();
session_register("login_check_number");
//昨晚看到了chianren上的驗(yàn)證碼效果,就考慮了一下,用PHP的GD庫(kù)完成了類似功能
//先成生背景,再把生成的驗(yàn)證碼放上去
$img_height=120;  //先定義圖片的長(zhǎng)、寬
$img_width=40;
if($HTTP_GET_VARS["act"]== "init"){
  //srand(microtime() * 100000);//PHP420后,srand不是必須的
  for($Tmpa=0;$Tmpa<4;$Tmpa++){
    $nmsg.=dechex(rand(0,15));
  }//by sports98
  $HTTP_SESSION_VARS[login_check_number] = $nmsg;
  //$HTTP_SESSION_VARS[login_check_number] = strval(mt_rand("1111","9999"));  //生成4位的隨機(jī)數(shù),放入session中
  //誰(shuí)能做下補(bǔ)充,可以同時(shí)生成字母和數(shù)字啊??----由sports98完成了
  $aimg = imageCreate($img_height,$img_width);  //生成圖片
  ImageColorAllocate($aimg, 255,255,255);      //圖片底色,ImageColorAllocate第1次定義顏色PHP就認(rèn)為是底色了
  $black = ImageColorAllocate($aimg, 0,0,0);    //定義需要的黑色
  ImageRectangle($aimg,0,0,$img_height-1,$img_width-1,$black);//先成一黑色的矩形把圖片包圍
  //下面該生成雪花背景了,其實(shí)就是在圖片上生成一些符號(hào)
  for ($i=1; $i<=100; $i++) {  //先用100個(gè)做測(cè)試
    imageString($aimg,1,mt_rand(1,$img_height),mt_rand(1,$img_width),"*",imageColorAllocate($aimg,mt_rand(200,255),mt_rand(200,255),mt_rand(200,255)));
    //哈,看到了吧,其實(shí)也不是雪花,就是生成＊號(hào)而已.為了使它們看起來"雜亂無章、5顏6色",就得在1個(gè)1個(gè)生成它們的時(shí)候,讓它們的位置、顏色,甚至大小都用隨機(jī)數(shù),rand()或mt_rand都可以完成.
  }
  //上面生成了背景,現(xiàn)在就該把已經(jīng)生成的隨機(jī)數(shù)放上來了.道理和上面差不多,隨機(jī)數(shù)1個(gè)1個(gè)地放,同時(shí)讓他們的位置、大小、顏色都用成隨機(jī)數(shù)~~
  //為了區(qū)別于背景,這里的顏色不超過200,上面的不小于200
  for ($i=0;$i<strlen($HTTP_SESSION_VARS[login_check_number]);$i++){
    imageString($aimg, mt_rand(3,5),$i*$img_height/4+mt_rand(1,10),mt_rand(1,$img_width/2), $HTTP_SESSION_VARS[login_check_number][$i],imageColorAllocate($aimg,mt_rand(0,100),mt_rand(0,150),mt_rand(0,200)));
  }
  Header("Content-type: image/png");  //告訴瀏覽器,下面的數(shù)據(jù)是圖片,而不要按文字顯示
  ImagePng($aimg);          //生成png格式...嘿嘿效果蠻像回事的嘛...
  ImageDestroy($aimg);
}
?>