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Supposedly, once you have verified authorship, Google should take it from there. I have tried adding direct links on posts to Google+: "Joakim Westman can be found on Google Plus" (which then links to the author's Google+ profile). The author biography pages on my site almost always come up in the serps with pictures, and I link those back to their Google+ pages as well. But really, my best indicator has been the more the author writes, the more they show up. As far as Google not trusting you, I'd look at the overall picture, not display in serps. Google is always messing around with display, for their own reasons.