PHP生成验证码图片 PHP生成验证码的原理：使用PHP的GD库，生成一张带验证码的图片，并将验证码保存在Session中。PHP生成验证码的大致流程有： 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
PHP生成验证码的原理：使用PHP的GD库，生成一张带验证码的图片，并将验证码保存在Session中。PHP生成验证码的大致流程有：
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破解验证码；
7、输出图片；
8、释放图片所占内存。
示例代码。
<code>
session_start();
getCode(<span>4</span>,<span>60</span>,<span>20</span>);
<span>function</span> getCode(<span>$</span><span>num</span>,<span>$</span><span>w</span>,<span>$</span><span>h</span>) {
<span>$</span><span>code</span> = <span>""</span>;
<span>for</span> (<span>$</span><span>i</span> = <span>0</span>; <span>$</span><span>i</span> $<span>num</span>; <span>$</span><span>i</span>++) {
<span>$</span><span>code</span> .= rand(<span>0</span>, <span>9</span>);
}
<span>//4位验证码也可以用rand(1000,9999)直接生成</span>
<span>//将生成的验证码写入session，备验证时用</span>
<span>$_SESSION</span>[<span>"helloweba_num"</span>] = <span>$</span><span>code</span>;
<span>//创建图片，定义颜色值</span>
header(<span>"Content-type: image/PNG"</span>);
<span>$</span><span>im</span> = imagecreate(<span>$</span><span>w</span>, <span>$</span><span>h</span>);
<span>$</span><span>black</span> = imagecolorallocate(<span>$</span><span>im</span>, <span>0</span>, <span>0</span>, <span>0</span>);
<span>$</span><span>gray</span> = imagecolorallocate(<span>$</span><span>im</span>, <span>200</span>, <span>200</span>, <span>200</span>);
<span>$</span><span>bgcolor</span> = imagecolorallocate(<span>$</span><span>im</span>, <span>255</span>, <span>255</span>, <span>255</span>);
<span>//填充背景</span>
imagefill(<span>$</span><span>im</span>, <span>0</span>, <span>0</span>, <span>$</span><span>gray</span>);
<span>//画边框</span>
imagerectangle(<span>$</span><span>im</span>, <span>0</span>, <span>0</span>, <span>$</span><span>w</span><span>-1</span>, <span>$</span><span>h</span><span>-1</span>, <span>$</span><span>black</span>);
<span>//随机绘制两条虚线，起干扰作用</span>
<span>$</span><span>style</span> = <span>array</span> (<span>$</span><span>black</span>,<span>$</span><span>black</span>,<span>$</span><span>black</span>,<span>$</span><span>black</span>,<span>$</span><span>black</span>,
<span>$</span><span>gray</span>,<span>$</span><span>gray</span>,<span>$</span><span>gray</span>,<span>$</span><span>gray</span>,<span>$</span><span>gray</span>
);
imagesetstyle(<span>$</span><span>im</span>, <span>$</span><span>style</span>);
<span>$</span><span>y1</span> = rand(<span>0</span>, <span>$</span><span>h</span>);
<span>$</span><span>y2</span> = rand(<span>0</span>, <span>$</span><span>h</span>);
<span>$</span><span>y3</span> = rand(<span>0</span>, <span>$</span><span>h</span>);
<span>$</span><span>y4</span> = rand(<span>0</span>, <span>$</span><span>h</span>);
imageline(<span>$</span><span>im</span>, <span>0</span>, <span>$</span><span>y1</span>, <span>$</span><span>w</span>, <span>$</span><span>y3</span>, IMG_COLOR_STYLED);
imageline(<span>$</span><span>im</span>, <span>0</span>, <span>$</span><span>y2</span>, <span>$</span><span>w</span>, <span>$</span><span>y4</span>, IMG_COLOR_STYLED);
<span>//在画布上随机生成大量黑点，起干扰作用;</span>
<span>for</span> (<span>$</span><span>i</span> = <span>0</span>; <span>$</span><span>i</span> 80; <span>$</span><span>i</span>++) {
imagesetpixel(<span>$</span><span>im</span>, rand(<span>0</span>, <span>$</span><span>w</span>), rand(<span>0</span>, <span>$</span><span>h</span>), <span>$</span><span>black</span>);
}
<span>//将数字随机显示在画布上,字符的水平间距和位置都按一定波动范围随机生成</span>
<span>$</span><span>strx</span> = rand(<span>3</span>, <span>8</span>);
<span>for</span> (<span>$</span><span>i</span> = <span>0</span>; <span>$</span><span>i</span> $<span>num</span>; <span>$</span><span>i</span>++) {
<span>$</span><span>strpos</span> = rand(<span>1</span>, <span>6</span>);
imagestring(<span>$</span><span>im</span>, <span>5</span>, <span>$</span><span>strx</span>, <span>$</span><span>strpos</span>, substr(<span>$</span><span>code</span>, <span>$</span><span>i</span>, <span>1</span>), <span>$</span><span>black</span>);
<span>$</span><span>strx</span> += rand(<span>8</span>, <span>12</span>);
}
imagepng(<span>$</span><span>im</span>);<span>//输出图片</span>
imagedestroy(<span>$</span><span>im</span>);<span>//释放图片所占内存</span>
}
</code>代码中,自定义函数getCode()诠释了验证码的生成过程。运用PHP GD库自带的图像处理函数，能轻松生成各种想要的图片效果。
imagecreate()：创建一个新图像
imagecolorallocate()：为图像分配颜色
imagefill()：填充图像
imagerectangle()：画一个矩形（边框）
imagesetstyle()：设置画线风格
imageline()：画一条线段
imagesetpixel()：画点像素
imagepng()：以PNG格式将图像输出到浏览器或文件
imagedestroy()：释放图片所占内存
将上述代码保存为code_num.php，以便调用。
验证码生成后，我们要在实际的项目中应用，通常我们使用ajax可以实现点击验证码时刷新生成新的验证码（有时生成的验证码肉眼很难识别），即“看不清换一张”。填写验证码后，还需要验证所填验证码是否正确，验证的过程是要后台程序来完成，但是我们也可以通过ajax来实现无刷新验证。
我们建立一个前端页面index.html，载入jquery，同时在body中加入验证码表单元素：
<code> <span><p><span>></span>验证码：<span><input> <span>type</span>=<span>"text"</span> <span>class</span>=<span>"input"</span> <span>id</span>=<span>"code_num"</span> <span>name</span>=<span>"code_num"</span> <span>maxlength</span>=<span>"4"</span> <span>/></span> <span><img alt="【代码实现】PHP生成各种随机验证码" > <span>src</span>=<span>"code_num.php"</span> <span>id</span>=<span>"getcode_num"</span> <span>title</span>=<span>"看不清，点击换一张"</span> <span>align</span>=<span>"absmiddle"</span><span>></span><span></span></span></span></p></span> <span><p><span>></span><span><input> <span>type</span>=<span>"button"</span> <span>class</span>=<span>"btn"</span> <span>id</span>=<span>"chk_num"</span> <span>value</span>=<span>"提交"</span> <span>/></span><span></span></span></p></span> </code>
html代码中，
<code>
$(<span>function</span>()<span>{</span>
<span>//数字验证</span>
$(<span>"#getcode_num"</span>).click(<span>function</span>()<span>{</span>
$(<span>this</span>).attr(<span>"src"</span>,<span>'code_num.php?'</span> + <span>Math</span>.random());
<span>}</span>);
...
<span>}</span>);
</code>刷新验证码，其实就是重新请求了验证码生成程序，这里要注意的是调用code_num.php时要带上随机参数防止缓存。接下来填写好验证码之后，点“提交”按钮，通过$.post()，前端向后台chk_code.php发送ajax请求。
<code>
$(<span>function</span>()<span>{</span>
...
$(<span>"#chk_num"</span>).click(<span>function</span>()<span>{</span>
<span>var</span> code_num = $(<span>"#code_num"</span>).val();
$.post(<span>"chk_code.php?act=num"</span>,<span>{</span>code:code_num<span>}</span>,<span>function</span>(msg)<span>{</span>
<span>if</span>(msg==<span>1</span>)<span>{</span>
alert(<span>"验证码正确！"</span>);
<span>}</span><span>else</span><span>{</span>
alert(<span>"验证码错误！"</span>);
<span>}</span>
<span>}</span>);
<span>}</span>);
<span>}</span>);
</code>后台chk_code.php验证：
<code>
session_start();
<span>$</span><span>code</span> = trim(<span>$_POST</span>[<span>'code'</span>]);
<span>if</span>(<span>$</span><span>code</span>==<span>$_SESSION</span>[<span>"helloweba_num"</span>]){
<span>echo</span> <span>'1'</span>;
}
</code>后台根据提交的验证码与保存在session中的验证码比对，完成验证。
对于其他几种验证的生成和使用，其原理一样，开发者可以根据需要，产生多种样式的随机验证码，本文演示demo中提供了数字验证码、数字+字母验证码、中文验证码、仿google验证码，算术验证码等。
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