Watermarking made DEAD SIMPLE (tutorial )

<?php
class watermark{
 
      # given two images, return a blended watermarked image
function create_watermark( $main_img_obj, $watermark_img_obj, $alpha_level = 100 ) {
      $alpha_level      /= 100;     # convert 0-100 (%) alpha to decimal
 
      # calculate our images dimensions
      $main_img_obj_w   = imagesx( $main_img_obj );
      $main_img_obj_h   = imagesy( $main_img_obj );
      $watermark_img_obj_w    = imagesx( $watermark_img_obj );
      $watermark_img_obj_h    = imagesy( $watermark_img_obj );
      
      # determine center position coordinates
      $main_img_obj_min_x     = floor( ( $main_img_obj_w) - ( $watermark_img_obj_w) );
      $main_img_obj_max_x     = ceil( ( $main_img_obj_w / 2 ) + ( $watermark_img_obj_w / 2 ) );
      $main_img_obj_min_y     = floor( ( $main_img_obj_h ) - ( $watermark_img_obj_h ) );
      $main_img_obj_max_y     = ceil( ( $main_img_obj_h / 2 ) + ( $watermark_img_obj_h / 2 ) ); 
      
      # create new image to hold merged changes
      $return_img = imagecreatetruecolor( $main_img_obj_w, $main_img_obj_h );
 
      # walk through main image
      for( $y = 0; $y < $main_img_obj_h; $y++ ) {
      for( $x = 0; $x < $main_img_obj_w; $x++ ) {
            $return_color     = NULL;
            
            # determine the correct pixel location within our watermark
            $watermark_x      = $x - $main_img_obj_min_x;
            $watermark_y      = $y - $main_img_obj_min_y;
            
            # fetch color information for both of our images
            $main_rgb = imagecolorsforindex( $main_img_obj, imagecolorat( $main_img_obj, $x, $y ) );
            
            # if our watermark has a non-transparent value at this pixel intersection
            # and we're still within the bounds of the watermark image
            if (  $watermark_x >= 0 && $watermark_x < $watermark_img_obj_w &&
                              $watermark_y >= 0 && $watermark_y < $watermark_img_obj_h ) {
                  $watermark_rbg = imagecolorsforindex( $watermark_img_obj, imagecolorat( $watermark_img_obj, $watermark_x, $watermark_y ) );
                  
                  # using image alpha, and user specified alpha, calculate average
                  $watermark_alpha  = round( ( ( 127 - $watermark_rbg['alpha'] ) / 127 ), 2 );
                  $watermark_alpha  = $watermark_alpha * $alpha_level;
            
                  # calculate the color 'average' between the two - taking into account the specified alpha level
                  $avg_red          = $this->_get_ave_color( $main_rgb['red'],            $watermark_rbg['red'],        $watermark_alpha );
                  $avg_green  = $this->_get_ave_color( $main_rgb['green'],      $watermark_rbg['green'],      $watermark_alpha );
                  $avg_blue         = $this->_get_ave_color( $main_rgb['blue'],      $watermark_rbg['blue'],       $watermark_alpha );
                  
                  # calculate a color index value using the average RGB values we've determined
                  $return_color     = $this->_get_image_color( $return_img, $avg_red, $avg_green, $avg_blue );
                  
            # if we're not dealing with an average color here, then let's just copy over the main color
            } else {
                  $return_color     = imagecolorat( $main_img_obj, $x, $y );
                  
            } # END if watermark
 
            # draw the appropriate color onto the return image
            imagesetpixel( $return_img, $x, $y, $return_color );
 
      } # END for each X pixel
} # END for each Y pixel 
            
      # return the resulting, watermarked image for display
      return $return_img;
 
} # END create_watermark()
      
      # average two colors given an alpha
      function _get_ave_color( $color_a, $color_b, $alpha_level ) {
      return round( ( ( $color_a * ( 1 - $alpha_level ) ) + ( $color_b  * $alpha_level ) ) );
} # END _get_ave_color()    
 
      # return closest pallette-color match for RGB values
    function _get_image_color($im, $r, $g, $b) {
      $c=imagecolorexact($im, $r, $g, $b);
      if ($c!=-1) return $c;
      $c=imagecolorallocate($im, $r, $g, $b);
      if ($c!=-1) return $c;
      return imagecolorclosest($im, $r, $g, $b);
} # EBD _get_image_color()

 
} # END watermark API
?>

<?php
$pic = $_GET['stb'];
$water = "watermark.gif";
$pic = "secret/$pic.jpg";
 
      # include our watermerking class
      include 'water.php';
      $watermark              = new watermark();
 

   $main_img_obj                       = imagecreatefromjpeg("$pic");
      $watermark_img_obj      = imagecreatefromgif("$water");


// writing text

 $words = "Hello This is example text";

// true type font
$font = 'font.ttf';


// size duh

$fontsize=13;
// color

$color = ImageColorAllocate($main_img_obj, 100, 0, 100);

// Where to place the text
// from top
$ft = "22";
//from right
$fr = "22";
// angle
$angle = "0";

imagettftext($main_img_obj,  $fontsize, $angle, $fr, $ft, $color, $font, $words );



      # create our watermarked image - set 66% alpha transparency for our watermark
      $return_img_obj               = $watermark->create_watermark( $main_img_obj, $watermark_img_obj, 66 );
 
      # display our watermarked image - first telling the browser that it's a JPEG, 
      # and that it should be displayed inline
      header( 'Content-Type: image/jpeg' );
      header( 'Content-Disposition: inline; filename=' . $_GET['src'] );
      imagejpeg( $return_img_obj, '', 50 );
 
?>

RewriteEngine on
 RewriteRule ^(.*)\.jpeg http://www.yoursite.com/script/?stb=$1 [nc]