According to Ted Stryk (a regularly featured imager) this image has been under construction for over a year (higher resolution available here). If you are unaware, to date… no color images have seen the light of day from the 1973 Mariner 10 encounter. So it is with unexpected shock that we are granted this fine image from an old encounter the night before we are expected to be dazzled with a plethora of new Messenger images.
Although different missions are handled differently than others, we may not be granted all images as soon as they are received here on Earth. For example, Cassini has its images open almost immediately through the raw files link… while ESA makes us wait (and still does) while they release “official” images and other reports to the press. The Cassini method is far greater an option as freelance imagers will get color composites up and available hours after an encounter while you may wait weeks for the official imaging team to get around to making color composites for public consumption. I fear the latter will be true of Messenger (especially as Mercury is not expected to be an overly colorful place), but most US based planetary missions have been great about sharing the wealth practically in real time… hopefully Messenger follows the trend.
So enjoy this for now — as stated by JRehling at unmannedspaceflight, “The best Mercury image in mankind's history -- for another week.”