本文实例讲述了PHP实现生成带背景的图形验证码功能。分享给大家供大家参考，具体如下：
以前我们利用PHP生成的都是无背景或同一色彩背景的验证码了,但这种验证容易给机器识别了,这里就来介绍一些生成带背景的图形验证码实例.
1、产生一张png的图片, 2、为图片设置背景色, 3、设置字体颜色和样式, 4、产生4位数的随机的验证码, 5、把产生的每个字符调整旋转角度和位置画到png图片上, 6、加入噪点和干扰线防止注册机器分析原图片来恶意注册, 7、输出图片, 8、释放图片所占内存
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PHP
session_start ();
header ( 'Content-type: image/png' );
//创建图片
$im = imagecreate($x=130,$y=45 );
$bg = imagecolorallocate($im,rand(50,200),rand(0,155),155)); //第一次对 imagecolorallocate() 的调用会给基于调色板的图像填充背景色
$fontColor = imageColorAllocate ( $im,255,255 ); //字体颜色
$fontstyle = 'rock.ttf'; //字体样式，这个可以从c:windowsFonts文件夹下找到，我把它放到和authcode.PHP文件同一个目录，这里可以替换其他的字体样式
//产生随机字符
for($i = 0; $i < 4; $i ++) {
$randAsciiNumArray = array (rand(48,57),rand(65,90));
$randAsciiNum = $randAsciiNumArray [rand ( 0,1 )];
$randStr = chr ( $randAsciiNum );
imagettftext($im,30,20)-rand(0,25),5+$i*30,rand(30,35),$fontColor,$fontstyle,$randStr);
$authcode .= $randStr;
}
$_SESSION['authcode'] = $randFourStr;//用户和用户输入的验证码做比较
//干扰线
for ($i=0;$i<8;$i++){
$lineColor = imagecolorallocate($im,255),255));
imageline ($im,$x),$y,$lineColor);
}
//干扰点
for ($i=0;$i<250;$i++){
imagesetpixel($im,$y),$fontColor);
}
imagepng($im);
imagedestroy($im);
?>
例2,新建一个PHP文件captcha_code_file.PHP,代码如下:
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//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);
$arr_text_color = hexrgb($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,$image_width),$image_height),2,3,$image_noise_color);
}
/* generating lines randomly in background of image */
for( $i=0; $i<$random_lines; $i++ ) {
imageline($image,$image_noise_color);
}
/* create a text box and add 6 letters code in it */
$textbox = imagettfbbox($font_size,$font,$code);
$x = ($image_width - $textbox[4])/2;
$y = ($image_height - $textbox[5])/2;
imagettftext($image,$font_size,$x,$text_color,$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);
}
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