It seems that the issue regarding Netra API callbacks returning "Malformed Image" is revolving around pbs.twimg.com (Twitter's CDN Service). An image can become available for a moment, and then become unavailable shortly after. The issue was brought up within the Twitter Development Community (See: pbs-twimg-com-cdn-problems). After a number of tests, Netra can also confirm that the issue persists today.
Using a browser, we tried to retrieve an image and it was not available.