Making all image caption links rel nofollow

Hi all,

I have found a few plugins that make ALL external links on a website nofollow but I’m look to make just image caption links nofollow.

Here is an example plugin that does not do the job I’m looking for:
https://www.ads-software.com/plugins/sem-external-links/
https://www.ads-software.com/plugins/mwb-wp-nofollow-links/

I found this piece of code but it’s not quite what I’m looking for and it’s for a specific theme I believe.
https://soliloquywp.com/docs/add-relnofollow-image-links/

When on the post edit page, clicking on an image in a post and editing it, you get a box come up https://pasteboard.co/HYFxDue.jpg
There is an area ‘link rel’. I believe a piece of code should be able to enter the value nofollow for all images using that box.

Any help would be greatly appreciated.

Many thanks