See Backlinks Footer for the code.

Solution for trailing commas from here: https://tiddlywiki.narkive.com/CyGQSaKC/tw-tw5-listwidget-comma-separated-output

This is another one: https://ryzn.me/wiki/Adding%2520Backlinks%2520to%2520TiddlyWiki.html

Conditional display is by checking to see if there is at least one backlink.

And an Image List! Formatting needs work. The image gallery example at TW has most of the details https://tiddlywiki.com/#ImageGallery%20Example