How can I remove image taxonomy pages from my theme and from Google?

Google is finding those pages because you’re linking to them. Most likely this happens when you use the media uploader and hit the “insert into post” button. Unless you tell it otherwise, WP will link to the attachment page intead of the image file. So head to your pages and remove the links to attachment pages.

I would not recommend you prevent google bot from indexing your images (as one answer suggests), that is not the issue. Plus getting traffic from image search is not a bad thing.

If you’re using a sitemap, ensure that the sitemap is not including the attachment pages.

After you’ve removed the links to attachment pages, you can “disable” attachment pages by hooking into template redirect like so:

<?php
add_action( 'template_redirect', 'wpse27119_template_redirect' );
function wpse27119_template_redirect()
{
    // get out of here if we're not headed to an attachment page    
    if( ! is_attachment() ) return; 

    // Find the $post variable representing the page where we're heading
    global $post;
    if( empty( $post ) ) $post = get_queried_object();

    // Find the permalink of our parent post
    $link = get_permalink( $post->post_parent );

    // redirect to the parent page
    wp_redirect( $link, 301 );
    exit(); // always call exit after wp_redirect
}

As a plugin: http://pastie.org/2443854