Media upload default linking (change the attachment link to none in wordpress)

This procedure will work for image media default linking in wordpress......

Place this in your theme's functions.php file.

function mytheme_setup() {
 // Set default values for the upload media box
 update_option('image_default_align', 'center' );
 update_option('image_default_link_type', 'media' );
 update_option('image_default_size', 'large' );

}
add_action('after_setup_theme', 'mytheme_setup');

If you want the default link action to be none, then change this line

update_option('image_default_link_type', 'none' );

Hope this helps and good luck