Most hosting services offer hotlink protection. Otherwise you need access to your document root .htaccess file
RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://yoursite/.*$ [NC]
RewriteCond %{HTTP_REFERER} !^http://yoursite$ [NC]
RewriteCond %{HTTP_REFERER} !^http://www.yoursite/.*$ [NC]
RewriteCond %{HTTP_REFERER} !^http://www.yoursite$ [NC]
RewriteRule .*\.(jpg|jpeg|gif|png|bmp)$ - [F,NC]
This is from one of my sites with hotlinking protection turned on. Needless to say, replace 'yoursite' with the url of your site.
What it does is prevent any site other than yours to access the image files.
There are other codes that can be added but this is a basic one.
