效果：

myvcode.class.php：封装创建验证码的类

<"mailto:*@param">*@param int $width         设置默认宽度
*@param int $height     设置默认高度
*@param int $codeNum    设置验证码中的字符个数
*@param int $pixNum        设置干扰点的个数
*@param int $lineNum    设置干扰线的数量
*/
function __construct($width=80,$height=40,$codeNum=4,$pixNum=40,$lineNum=5)
{
$this->width = $width;
$this->height = $height;
$this->codeNum = $codeNum;
$this->pixNum = $pixNum;
$this->lineNum = $lineNum;
}
/*内部私有方法,创建图像资源*/
private function getCreateImage()
{
$this->image = imagecreatetruecolor($this->width, $this->height);
$white = imagecolorallocate($this->image,0xff,0xff,0xff);
imagefill($this->image, 0, 0, $white);
$black = imagecolorallocate($this->image,0,0,0);
imagerectangle($this->image, 0, 0, $this->width-1, $this->height-1, $black);
}
/*内部私有方法,绘制字符，去掉o0Llz和012*/
private function createCheckCode()
{
$code = '3456789abcdefghijkmnpqrstuvwxyABCDEFGHIJKMNPQRSTUVWXY';
$this->checkCode = "";
for($i=0; $i<$this->codeNum;$i++)
{
$char = $code{rand(0,strlen($code) - 1)};
$this->checkCode .= $char;
$fontColor = imagecolorallocate($this->image, rand(0,128), rand(0,128),rand(0,128));
$fontSize = rand(3,5);
$x = rand(0,$this->width-imagefontwidth($fontSize));
$y = rand(0,$this->height-imagefontheight($fontSize));
imagechar($this->image, $fontSize, $x, $y, $char, $fontColor);
}
}
/*内部私有方法设置干扰元素*/
private function setDisturbColor()
{
/*绘制干扰点*/
for($i=0; $i<$this->pixNum; $i++)
{
$color = imagecolorallocate($this->image, rand(0,255), rand(0,255), rand(0,255));
imagesetpixel($this->image, rand(1,$this->width-2), rand(1,$this->height-2), $color);
}
/*绘制干扰线*/
for($i=0; $i<$this->lineNum; $i++)
{
$color = imagecolorallocate($this->image, rand(0,255), rand(0,255), rand(0,255));
imageline($this->image, rand(1,$this->width / 2), rand(1,$this->height / 2),
rand($this->width / 2,$this->width – 2), rand($this->height / 2,$this->height – 2), $color);