新建一个PHP文件captcha_code_file.php

//首先开启session
session_start();
//定义前台显示验证码长&宽
$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";
//定义要生成验证码的字符串
$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
//设置session,做验证
$_SESSION['6_letters_code'] = $code;

function hexrgb ($hexstr)
{
$int = hexdec($hexstr);

return array("red" => 0xFF & ($int >> 0x10),
"green" => 0xFF & ($int >> 0x8),
"blue" => 0xFF & $int);
}

调用页面显示验证码页面index.php

<?php
session_start();
if(isset($_REQUEST['Submit'])){
// code for check server side validation
if(empty($_SESSION['6_letters_code'] ) ||
strcasecmp($_SESSION['6_letters_code'], $_POST['6_letters_code']) != 0)
{
$msg="您输入的验证码有误,请重新输入!";
}else{
echo "您输入的是正确的!";
// 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"> 验证码Demo:</td>
<td><img src="captcha_code_file.php?rand=<?php echo rand(0,20);?>" id='captchaimg' onclick="refreshCaptcha();" ><br>
<label for='message'>请输入验证码:</label>
<br>
<input id="6_letters_code" name="6_letters_code" type="text">
<br>
如果看不到,请 <a href='javascript: refreshCaptcha();'>点我</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'>
//定义的刷新请求
function refreshCaptcha()
{
var img = document.images['captchaimg'];
img.src = img.src.substring(0,img.src.lastIndexOf("?"))+"?rand="+Math.random()*1000;
}
</script>

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