There are a few ways to post pictures of your rig in the Rig Showcase Space. One way is by clicking the Edit button and add a photo in the area below the description once you've created your post. Another way, which I think it's a bit easier and quicker, is my uploading the photo while you're creating the post. Just import/upload it in the "Description" section of the form. Either way, be sure to delete the instruction text.