Disclaimer: to properly read the following article, you need to have a pair of red-cyan 3D glasses, otherwise the images won't display as intended. The cheapest one should do it, perhaps even home made. Lacking such glasses, you can generate your own 3D images for different types of glasses.
A few weeks ago I stumbled upon an old article about how James Cameron is/was remaking Titanic in 3D and somewhere in the technical explanation it was mentioned you can do 2D to 3D conversion with Free Software tools, namely the G'MIC plugin for GIMP.
In the late '90ies I received a computer magazine which came with a pair of paper 3D glasses and a CD containing the usual software demos AND a few 3D pictures, it was my first contact with anaglyphs. I still have the glasses, but I use them maybe once every few years, when I remember to search some such images.
Along the time I learned how to properly make such images: two cameras, filters, combine the two images in one. Way too much effort for me. It looks like way too much effort even for some commercial filmmakers...
When I saw the Titanic article, I said to myself 'what the heck, let give G'MIC a try'. AFAIK it is not available in any official Fedora repo, but you can download a binary from the upstream, drop it in the proper folder and go with it. It will survive even a distro update/reinstall. Not a big fan of the 'application inside another application' approach of G'MIC, nor of its duplication of existing GIMP features, that's why didn't have it already installed, but playing is fun.
I don't have the time and patience to learn how to fine-tune the parameters (with hand crafted depth maps you should be able to reach high quality results), nor do I plan to return to anaglyphs any time soon, so I used pretty much the automatic settings. Below are a few pictures I think came decently with no fiddling and automatic settings: