Half-life 2: Episode 3 concept art has apparently made its way on to the web via ValveTime.net. I’ll leave it up to you to decide if they’re legit although the site has claimed, “We wouldn’t post anything unless it was 100% confirmed”.
The images are apparently from 2008 and seem to feature a variety of costumes for Alyx and Gordon, as well as some Combine soldiers. The icey theme ties into the Borealis, a near mythical ship carrying powerful technology that vanished and is supposed to be stranded in the Arctic somewhere. It’s been referenced in Half-life Episode 1, 2 and Portal 2.
ValveTime.net stated on their Facebook page, “We wouldn’t post anything unless it was 100% confirmed. Sometimes we post things with a question mark at the end. This isn’t one of them. This is official (albeit old) Valve concept art for Episode 3″. They also said, “All the pictures are real. The concept art is supposed to be Alyx”.