How To Set Default Attachment Display Settings In WordPress
Whenever you insert an image from the WordPress’ media uploader, it allows you to set the attachment display settings in the right side of the pop-up modal. You always have to customize the display settings and it wastes a lot of time.

Here is a great code to set default attachment display settings by using your theme's functions.php file. Add following snippet to your theme's functions.php file:

PHP Code:
add_action'after_setup_theme''default_attachment_display_settings' );
/** 
* Set the Attachment Display Settings "Link To" default to "none" *
 * This function is attached to the 'after_setup_theme' action hook. *
**/
function default_attachment_display_settings()
 {    
update_option'image_default_align''left' );
    
update_option'image_default_link_type''none' );
    
update_option'image_default_size''large' );

Here are the options for each:
image_default_align

  • left
  • right
  • center
  • none

image_default_link_type

  • file
  • post
  • custom
  • none

image_default_size

  • thumbnail
  • medium
  • large
  • full

If you want the default link action to be none, then change this line
Code:
update_option('image_default_link_type', 'none' );