This thin, diminishing crescent is Venus. It was taken by Akatsuki about exactly two days after the spacecraft flew past Venus instead of entering orbit.
Bye bye, Venus, we're very sorry to have missed you. According to the Yomiuri Shimbun newspaper, the photos were taken with Akatsuki about 600,000 kilometers from Venus.
This image is actually good news, although it's little consolation: it's proof positive that the science instruments are healthy. They actually tested three of the cameras: one that takes images in ultraviolet, two in infrared. The images were posted here (text in Japanese, but the images speak for themselves). The images are very similar to the Akatsuki departure shots of Earth, taken less than seven months ago.
ISAS / JAXA
Akatsuki's cameras were working fine two days after it flew past Venus; these three images were taken with the UV1, IR1, and LIR cameras, respectively. The UV1 and IR1 cameras take images in wavelengths where the available light is from the Sun, so they viewed Venus as a crescent. The LIR camera is at a longer wavelength where Venus emits heat, so sees all of the planet's atmosphere glowing with thermal radiation. The UV1 and IR1 images are artificially colorized.
It happened that Venus scientist David Grinspoon, who was one of several American co-investigators recently named to be participants on the Akatsuki team, was on Facebook when I saw these images being posted by numerous Japanese space fans. I asked him what he thought about them, and he said, "Well, my initial reaction is that they are poignant and heartbreaking." He went on: "To have a perfectly functioning spacecraft with all those great instruments make it all that way across the depths, and then because of some problem with a 12 minute operation, to go sailing off back into the blackness..."
How beautiful, yet awful!
These images were released during a press briefing held in the last couple of hours, in which more details were evidently discussed about the thruster anomaly. Unfortunately the machine translations of the Tweets from the conference are just not quite good enough for me to understand what they are saying, although I get a sense that there was something hopeful being said about the main thruster. Some of the people Tweeting the conference were @yimamura, @ots_min, @ShinyaMatsuura, and @koumeiShibata. @yimamura in particular posted several images of slides from the press conference, while Shin-ya Matsuura posted a detailed writeup on his blog. There is also a page full of slides on a JAXA site here but Google can't translate the text in the images so I have no idea what they say! Hopefully by tomorrow morning my time, someone will have stepped up to do some translation that I can understand. I will unfortunately be busy most of the day as it's my older daughter's big Christmas show at school but I will try to tune in and figure out what is happening with Akatsuki when I can.
Meanwhile, @tsugumi_shirai has posted a "mission patch" for Akatsuki's six-year mission to return to Venus. Hope springs eternal!