The /imagelibrary/ folder appears to be outside of the WordPress website folder/URL structure / the htaccess heirarchical structure. ie it is not a parent to child heirarchy/structure and is instead a child to child folder structural relationship. Probably the simplest thing to do would be to create an .htaccess file in the /imagelibrary/ folder with rules about which referers can link to images or you could just allow any/all sites to link to these images by using a RewriteEngine Off htaccess file.
What is in the /imagelibrary/ folder? Is it a 3rd party application? Is it just a plain folder for storing images? Is there a particular reason you are using this /imagelibrary/ folder instead of the WordPress /uploads/ folder to store images?