order allow,deny
deny from 255.0.0.0
allow from all

This denies access to the IP 255.0.0.0.

order allow,deny
deny from 123.45.6.
allow from all

This denies access to all IPs in the range 123.45.6.0 to 123.45.6.255.

RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www\.)?yourdomain.com/.*$ [NC]
RewriteRule \.(gif|jpg|css)$ - [F]

This blocks all the links to '.gif', '.jpg' and '.css' files which are not from the domain name http://www.yourdomain.com.

Display alternate content:

RewriteEngine on
RewriteCond %{HTTP_REFERER} !^$
RewriteCond %{HTTP_REFERER} !^http://(www\.)?yourdomain.com/.*$ [NC]
RewriteRule \.(gif|jpg)$ http://www.yourdomain.com/angryman.jpg [R,L]

This blocks all links to '.gif' and '.jpg' files which are not from the domain name 'http://www.yourdomain.com/' and displays the file 'http://www.yourdomain.com/angryman.jpg' instead.

# Deny access to a directory from the IP 255.0.0.0
<Directory /path/to/directory>
    order allow,deny
    deny from 255.0.0.0
    allow from all
</Directory>

# Deny access to a file from the IP 255.0.0.0
<FilesMatch "^\.ht">
    order allow,deny
    deny from 255.0.0.0
    allow from all
</FilesMatch>