Wheel Condition Check
Curiosity Rover used its Hand Lens Imager (MAHLI) around 4 pm (local time) during mission Sol 1355, May 29, 2016 to acquire a set of images of its wheels. These were periodic checks to allow the rover's engineers to assess the accumulated wear and tear to its 6 aluminum wheels.
The MAHLI camera is located on the end of the rover's 2-meter long robotic arm. Images of the wheels are acquired by extending the arm away from the rover and then lowering it close to the ground.
I have corrected the rotation of the image and enhanced the colours a little.
For scale the rovers wheel diameter is 50 centimeters or about 20 inches, width is 40 centimeters, or 16 inches The distant base of the Gale crater rim mountains, seen at the top of this image were ~30 kilometers (~19 miles) from the rover's location in May 2016.
I thought this was a screenshot from Elite Dangerous for a second there.