php图片加水印原理（超简单的实例代码）

//文字水印:
$w = 80;
$h = 20;

$im = imagecreatetruecolor($w,$h);

$textcolor = imagecolorallocate($im, 123, 12, 255);

$white = imagecolorallocate($im, 255, 255, 255);
$grey = imagecolorallocate($im, 128, 128, 128);
$black = imagecolorallocate($im, 0, 0, 0);
imagefilledrectangle($im, 0, 0, 399, 29, $grey);      //画一矩形并填充

// 把字符串写在图像左上角
imagestring($im, 3, 2, 3, "Hello world!", $textcolor);

// 输出图像
header("Content-type: image/jpeg");
imagejpeg($im);
imagedestroy($im);

//图片水印

$groundImg = "DSC05940.jpeg";
$groundInfo = getimagesize($groundImg);
$ground_w = $groundInfo[0];
//print_r($groundInfo);
$ground_h = $groundInfo[1];
switch($groundInfo[2]){
case 1:
$ground_im = imagecreatefromgif($groundImg);
break;
case 2:
$ground_im = imagecreatefromjpeg($groundImg);
break;
case 3:
$ground_im = imagecreatefrompng($groundImg);
break;
}

$waterImg = "DSC05949.jpeg";
$imgInfo =getimagesize($waterImg);
$water_w = $imgInfo[0];
$water_w = $imgInfo[1];

switch($imgInfo[2]){
case 1:
$water_im = imagecreatefromgif($waterImg);
break;
case 2:
$water_im = imagecreatefromjpeg($waterImg);
break;
case 3:
$water_im = imagecreatefrompng($waterImg);
break;
}
imagecopy($ground_im,$water_im,100,100,0,0,500,500); 
header("Content-type: image/jpeg");

imagejpeg($ground_im);