Prevent hotlinking with .htaccess

RewriteEngine on
//Disallow blank referrers, but I recommend to not use it.
RewriteCond %{HTTP_REFERER} !^$ [NC,OR]
//Sites allowed to link your images
RewriteCond %{HTTP_REFERER} !^http(s)?://(www\.)?yourdomain.com [NC,OR]
RewriteCond %{HTTP_REFERER} !^http(s)?://(www\.)?yourdomain2.com [NC]
//Change ‘http://hpmouse.googlepages.com/hotlink.gif‘ to a image you’ve set, and whenever image hotlinking is detected,
RewriteRule \.(jpg|jpeg|png|gif)$ http://hpmouse.googlepages.com/hotlink.gif [NC,R,L]

Sign your hotlinks - Watermark on the Fly in PHP

Yon need PHP 4+ and GD 2.0+ on your server

<?php  

header('content-type: image/jpeg');  

$watermark = imagecreatefrompng('watermark.png');  

$watermark_width = imagesx($watermark);  

$watermark_height = imagesy($watermark);  

$image = imagecreatetruecolor($watermark_width, $watermark_height);  

$image = imagecreatefromjpeg($_GET['src']);  

$size = getimagesize($_GET['src']);  

$dest_x = $size[0] - $watermark_width - 5;  

$dest_y = $size[1] - $watermark_height - 5;  

imagecopymerge($image, $watermark, $dest_x, $dest_y, 0, 0, $watermark_width, $watermark_height, 100);  

imagejpeg($image);  

imagedestroy($image);  

imagedestroy($watermark);  

?>

“RewriteCond $1 ^.*.(jpg|jpeg|gif|png|bmp)$”

Or with no rewritecond the rewriterule should be:

“RewriteRule ^.*.(jpg|jpeg|gif|png|bmp)$ /scripts/watermark.php?src=%{REQUEST_URI} [L]”