.htaccess - Addon domain and .htaccess file redirect

Question

I have two domains:

1. maindomain.com
2. www.addondomain.com

A .htaccess file in maindomain.com has this redirect

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^www\.(([a-z0-9_]+\.)?maindomain\.com)$ [NC]
RewriteRule .? http://%1%{REQUEST_URI} [R=301,L]

It redirects www to non www version.

Another .htaccess file in addondomain.com have these redirect

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^addondomain.com$
RewriteRule ^(.*)$ "http\:\/\/www\.addondomain\.com\/$1" [R=301,L]
RewriteCond %{HTTP_HOST} ^addondomain\.maindomain\.com$ [OR]
RewriteCond %{HTTP_HOST} ^www\.addondomain\.maindomain\.com$
RewriteRule ^(.*)$ "http\:\/\/www\.addondomain\.com\/$1" [R=301,L]
RewriteCond %{HTTP_HOST} ^maindomain\.com$ [OR]
RewriteCond %{HTTP_HOST} ^www\.maindomain\.com$
RewriteRule ^(.*)$ "http\:\/\/www\.addondomain\.com\/$1" [R=301,L]

All pages redirect well, but when I put another .htaccess file in a subdirectory, the redirect does not work. So, I write these rules in image subdirectory.

RewriteCond %{HTTP_HOST} ^addondomain.com$
RewriteRule ^(.*)$ "http\:\/\/www\.addondomain\.com\/$1" [R=301,L]
RewriteCond %{HTTP_HOST} ^addondomain\.maindomain\.com$ [OR]
RewriteCond %{HTTP_HOST} ^www\.addondomain\.maindomain\.com$
RewriteRule ^(.*)$ "http\:\/\/www\.addondomain\.com\/$1" [R=301,L]
RewriteCond %{HTTP_HOST} ^maindomain\.com$ [OR]
RewriteCond %{HTTP_HOST} ^www\.maindomain\.com$
RewriteRule ^(.*)$ "http\:\/\/www\.addondomain\.com\/$1" [R=301,L]

Now when I try to access addondomain.maindomain.com/image/1.png it redirects to addondomain.maindomain.com/1.png with a 404 error. Some how, the image directory is lost. I need another .htaccess file in subdirectory.

UPDATE#1: addondomain is subdomain of maindomain also, directory structure is:

/public_html
    .htaccess
    home.php (page of main domain)
    /addondomain.com (directory)
        home.php (page of addondomain)
        .htaccess
        /image (directory)
            .htaccess
            1.png

UPDATE#2:

This works if I set .htaccess like this:

RewriteCond %{HTTP_HOST} ^(www\.)?maindomain\.com$ [NC]
RewriteRule ^(.*)$ http://www.addondomain.com/image/$1 [R=301,L]
RewriteCond %{HTTP_HOST} ^addondomain.com$
RewriteRule ^(.*)$ http://www.addondomain.com/image/$1 [R=301,L]
RewriteCond %{HTTP_HOST} ^addondomain\.maindomain\.com$ [OR]
RewriteCond %{HTTP_HOST} ^www\.addondomain\.maindomain\.com$
RewriteRule ^(.*)$ http://www.addondomain.com/image/$1 [R=301,L]

Is there any way to using some code (I am bit new) in place of image like

RewriteRule ^(.*)$ http://www.addondomain.com/.*$/$1 [R=301,L]