This particular image was acquired on 21 April 2015 with the Narrow Angle Camera. The image scale is only 5 km / 3 miles across and the resolution is 5 meters/pixel and every day the resolution is increasing as the spacecraft’s altitude decreases.
The impact is very close. After a successful Orbit Correction Maneuver planned for tomorrow (24 April 2015) the MESSENGER spacecraft will impact the surface of Mercury on 30 April 2015 between 19:25 and 19:30 UTC. That time is just a good estimate, impact time depends on how the correction maneuver goes and could be either a bit earlier or even up to one orbit later (8.3 hours). The time will surely be more certain after the correction maneuver tomorrow.
Impact confirmation will be the inability to establish communication between the spacecraft and Earth-based tracking systems.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington