compression/quality reduction filter?

[rich2005]

It will very much depend on your degraded image, there might be more than just jpeg artifacts to play with.

Not much available on creating artifacts other than exporting an image a couple of times with low jpeg quality settings.

There is a filter in the gmic plugin http://www.gmic.eu The latest version is a bit picky about installation

see: https://www.gimp-forum.net/Thread-Instal...ws-10-demo

edit: I see you are using linux. Dead easy, get one of the zips, unpack, pop the gmic_gimp_qt file in your Gimp profile ~/.gimp-2.8/plug-ins

At least it gives a preview for the result. This before/after