It is now possible to add other statements than just Depicts statements to files on Wikimedia Commons. How does this work? See below for a few examples of Wikimedia Commons files described with structured data.
A simple case
This photo of sugar cubes has captions in many different languages:
It has a Depicts statement (it depicts sugar cubes) with a few qualifiers (twelve sugar cubes in the color white). You can see this statement (and others) by clicking on the Structured data tab in the file page.
In addition, the file also has various other statements, indicating the license, creator and quality assessment.
A file showing a two-dimensional artwork
This file is a faithful digital representation of a two-dimensional artwork: Jan Bruegel the Elder's The Last Judgement (1602), collection Statens Museum for Kunst.
To indicate that, it has the following structured data statement, pointing to the Wikidata item for that specific artwork:
How can you help?
The two above examples are among the very first Wikimedia Commons files with structured data. Their structured data is still very incomplete. Just like in the early days of Wikidata, the data model for such files (which fields and properties are needed) is not fully established yet. Especially for GLAM files, a lot of thinking is welcome to build best practices on how to describe them properly with structured data. You can help in the following ways:
Experiment and add structured data to existing uploaded files, and think what kind of data (Wikidata properties and items) you need for that
Contribute to data modelling discussions. You can check the properties table on Wikimedia Commons to see if the community has already been discussing the kind of data you are interested in. And you can engage on its talk page if you want to discuss and ask questions.