Example output:
"batchcomplete": "",
"query": { "pages": { "41374178": { "pageid": 41374178, "ns": 0, "title": "Arya Stark", "contentmodel": "wikitext", "pagelanguage": "en", "pagelanguagehtmlcode": "en", "pagelanguagedir": "ltr", "touched": "2017-07-18T08:06:43Z", "lastrevid": 791120824, "length": 27902, "pageprops": { "defaultsort": "Stark, Arya", "page_image_free": "Arya_Stark-Maisie_Williams.jpg", "wikibase_item": "Q3624677"
In that output:
"page_image_free": "Arya_Stark-Maisie_Williams.jpg",
That media file is not a free use media, and is declared as such on the media page