php生成图片验证码的实例讲解

<div class="demo">
 <h3>1、数字验证码</h3>
 <p>验证码：<input type="text" class="input" id="code_num" name="code_num" maxlength="4" /> <img src="code_num.php" id="getcode_num" title="看不清，点击换一张" align="absmiddle" /></p>
 <p><input type="button" class="btn" id="chk_num" value="提交" /></p>
 </div>
 <div class="demo">
 <h3>2、数字+字母验证码</h3>
 <p>验证码：<input type="text" class="input" id="code_char" maxlength="4" /> <img src="code_char.php" id="getcode_char" title="看不清，点击换一张" align="absmiddle" /></p>
 <p><input type="button" class="btn" id="chk_char" value="提交" /></p>
 </div>
 <div class="demo">
 <h3>3、中文验证码</h3>
 <p>验证码：<input type="text" class="input" id="code_zh" maxlength="4" /> <img src="code_zh.php" id="getcode_zh" title="看不清，点击换一张" align="absmiddle" /></p>
 <p><input type="button" class="btn" id="chk_zh" value="提交" /></p>
 </div>
 <div class="demo">
 <h3>4、仿google验证码</h3>
 <p>验证码：<input type="text" class="input" id="code_gg" maxlength="4" /> <img src="code_gg.php" id="getcode_gg" title="看不清，点击换一张" align="absmiddle" /></p>
 <p><input type="button" class="btn" id="chk_gg" value="提交" /></p>
 </div>
 <div class="demo">
 <h3>5、算术验证码</h3>
 <p>验证码：<input type="text" class="input" id="code_math" maxlength="4" /> <img src="code_math.php" id="getcode_math" title="看不清，点击换一张" align="absmiddle" /></p>
 <p><input type="button" class="btn" id="chk_math" value="提交" /></p>
</div>

$(function() {
 $("#getcode_num").click(function() { //数字验证
  $(this).attr("src", 'code_num.php?' + Math.random());
 });
 $("#chk_num").click(function() {
  var code_num = $("#code_num").val();
  $.post("chk_code.php?act=num", {
   code: code_num
  },
  function(msg) {
   if (msg == 1) {
    alert("验证码正确！");
   } else {
    alert("验证码错误！");
   }
  });
 });
 //数字+字母验证
 $("#getcode_char").click(function() {
  $(this).attr("src", 'code_char.php?' + Math.random());
 });
 $("#chk_char").click(function() {
  var code_char = $("#code_char").val();
  $.post("chk_code.php?act=char", {
   code: code_char
  },
  function(msg) {
   if (msg == 1) {
    alert("验证码正确！");
   } else {
    alert("验证码错误！");
   }
  });
 });
 //中文验证码
 $("#getcode_zh").click(function() {
  $(this).attr("src", 'code_zh.php?' + Math.random());
 });
 $("#chk_zh").click(function() {
  var code_zh = escape($("#code_zh").val());
  $.post("chk_code.php?act=zh", {
   code: code_zh
  },
  function(msg) {
   if (msg == 1) {
    alert("验证码正确！");
   } else {
    alert("验证码错误！");
   }
  });
 });
 //google验证
 $("#getcode_gg").click(function() {
  $(this).attr("src", 'code_gg.php?' + Math.random());
 });
 $("#chk_gg").click(function() {
  var code_gg = $("#code_gg").val();
  $.post("chk_code.php?act=gg", {
   code: code_gg
  },
  function(msg) {
   if (msg == 1) {
    alert("验证码正确！");
   } else {
    alert("验证码错误！");
   }
  });
 });
 //算术验证
 $("#getcode_math").click(function() {
  $(this).attr("src", 'code_math.php?' + Math.random());
 });
 $("#chk_math").click(function() {
  var code_math = $("#code_math").val();
  $.post("chk_code.php?act=math", {
   code: code_math
  },
  function(msg) {
   if (msg == 1) {
    alert("验证码正确！");
   } else {
    alert("验证码错误！");
   }
  });
 });
});

session_start();
getCode(4,60,20);

function getCode($num,$w,$h) {
 $code = "";
 for ($i = 0; $i < $num; $i++) {
  $code .= rand(0, 9);
 }
 //4位验证码也可以用rand(1000,9999)直接生成
 //将生成的验证码写入session，备验证时用
 $_SESSION["helloweba_num"] = $code;
 //创建图片，定义颜色值
 header("Content-type: image/PNG");
 $im = imagecreate($w, $h);
 $black = imagecolorallocate($im, 0, 0, 0);
 $gray = imagecolorallocate($im, 200, 200, 200);
 $bgcolor = imagecolorallocate($im, 255, 255, 255);
 //填充背景
 imagefill($im, 0, 0, $gray);

 //画边框
 imagerectangle($im, 0, 0, $w-1, $h-1, $black);

 //随机绘制两条虚线，起干扰作用
 $style = array ($black,$black,$black,$black,$black,
  $gray,$gray,$gray,$gray,$gray
 );
 imagesetstyle($im, $style);
 $y1 = rand(0, $h);
 $y2 = rand(0, $h);
 $y3 = rand(0, $h);
 $y4 = rand(0, $h);
 imageline($im, 0, $y1, $w, $y3, IMG_COLOR_STYLED);
 imageline($im, 0, $y2, $w, $y4, IMG_COLOR_STYLED);

 //在画布上随机生成大量黑点，起干扰作用;
 for ($i = 0; $i < 80; $i++) {
  imagesetpixel($im, rand(0, $w), rand(0, $h), $black);
 }
 //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
 $strx = rand(3, 8);
 for ($i = 0; $i < $num; $i++) {
  $strpos = rand(1, 6);
  imagestring($im, 5, $strx, $strpos, substr($code, $i, 1), $black);
  $strx += rand(8, 12);
 }
 imagepng($im);//输出图片
 imagedestroy($im);//释放图片所占内存
}