Maybe that widget doesn't appear if the wiki has had no newly uploaded images?

I just uploaded 3 different images for 3 different pages, but nothing is showing up.

Maybe it requires some time for it to show up, like if depended on some cache?

It shouldn't be, because big wikis don't all have Recent Images on the rail. otherwise they would all have it, because from what I know, recent images just simply display images that have been posted to the page recently.

Unfortunately there hasn't been any official blog post talking about this widget. I know people started asking about it from May of this year, and none of those who replied know much about it, except Brandon (Fandom staff) who added a couple of comments on here:

     "The goal of Recent Images is quick visual engagement, rather than contribution (like uploads) or diving deep into what could be a confusing Special page for many users who are not as familiar with wiki editing."

The rest of his replies just goes on about not adding an upload button, as seen on another widged maintained by users on the Dev Wiki. But from there we can understand that Fandom made an experiment with this new feature, and that for now they consider it stable, and don't plan to make any changes to it:

     "We saw a good success rate in terms of people using Recent Images in the experiment, so for anything we added we'd have to make sure it didn't have a negative impact on how it's used."

If you're still curious about this feature, or if you think it's not working properly, I'd recommend you ask staff for details.

This from Gourge Fandom Support

"The team have let me know that it should show up when your wiki has more image activity - i..e more uploads total, more recent uploads, and the uploaded images need to be used on articles."

But I don't think it's like that, even the wiki that uploaded the last photo in 2 weeks also still shows Recent Images.

Well, at least now we know how it's supposed to work. Thanks for sharing!

@Livy Caldwell I think enough images for the rail to fill need to be uploaded before it’ll appear. Otherwise once it’s full it’ll update when new images are added but if none are added for a while it’ll just display the latest uploaded images (It can also be rather slow at times on my home Wiki when batch creating pages with images a few months ago the rail would take about half an hour to an hour before it decided it was ready to update).