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);
 $gray = imagecolorallocate($im,200,200);
 $bgcolor = imagecolorallocate($im,255,255);
 //填充背景
 imagefill($im,$gray);
 //画边框
 imagerectangle($im,$w-1,$h-1,$black);
 //随机绘制两条虚线,起干扰作用
 $style = array ($black,$black,$gray,$gray
 );
 imagesetstyle($im,$style);
 $y1 = rand(0,$h);
 $y2 = rand(0,$h);
 $y3 = rand(0,$h);
 $y4 = rand(0,$h);
 imageline($im,$y1,$y3,IMG_COLOR_STYLED);
 imageline($im,$y2,$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,$w),$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
}