If others are increasing your bandwidth by linking back to your images you can use this Apache re-write rule for preventing this activity on your site. Open your .htaccess file and add the following lines replacing sangkrit.com with your own domain name:
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} .(gif|jpe?g|png)$ [NC] RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !(www.)?sangkrit.com [NC] RewriteCond %{HTTP_REFERER} !google. [NC] RewriteCond %{HTTP_REFERER} !search?q=cache [NC] RewriteRule (.*) – [F,NC,L]