I found the below two functions/hooks to add a custom field to my gallery window. It seems to work, but I am now having issues getting the meta info and adding it to my post. I was thinking I could use apply_filters() functions, but am not quite sure on the parameters I need to use.
I was thinking something like this, but it is not right.
$imageLink = apply_filters('_rt-image-link', $attachment->_rt-image-link);
Any help would be greatly appreciated!!!
Here are the two functions that I added to my functions.php file.