Code:
RewriteEngine On
RewriteCond %{HTTP_REFERER} !^$ [NC]
RewriteCond %{HTTP_REFERER} !.*?domaina.com.* [NC]
RewriteCond %{HTTP_REFERER} !.*?domainb.com.* [NC]
RewriteCond %{HTTP_REFERER} !.*?domainc.com.* [NC]
RewriteRule .*\.(gif|GIF|jpg|JPG)$ http://domain.com/bad.gif [R,L]