The Structured Data on Commons development team has the very basic version of depicts statements available for early testing on Test-Commons. You can add very basic depicts statements to the file page by going into the new “Structured Data” tab located below the "Open in Media Viewer button." You can use the Latest Files link in the left side nav bar to select existing images, or use the UploadWizard to upload new ones to test with (although those images won’t actually show up on the site). The test site is not a fully functional replica of Commons, so there may be some overall problems in using the site, but you should be able to get a general idea of what using the feature is like.
Early next week I will call for broad, community-wide testing of the feature similar to what we did for Captions, with instructions for testing, known bugs, and a dedicated space to discuss the feature as well as a simple help page for using statements. Until then, you're welcome to post on the SDC talk page with what you might find while testing depicts.