This Pro tutorial provides the steps for outputting values of custom fields for the featured image of current post in a Bricks query loop.
Consider this sample field group created using ACF:
Field label: Original SourceField type: URLLocation: Attachment = All

After implementing the tutorial:

Notice the ORIGINAL SOURCE link for the featured images with the field populated. It links to the value (in this case, a URL) set for the images.

Step 1
Using your favorite custom fields plugin create a custom field for either all attachments or image-type of attachments.
Edit your posts' featured images and populate your custom field.
Step 2
Add the following in child theme's functions.php (w/o the opening PHP tag) or a code snippets plugin:
This is a BricksLabs Pro tutorial.
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