The rover does a little nadir-gazing. The MARDI camera, used originally to record the final part of Curiosity’s entry, descent, and landing, is sometimes used to image the ground directly under the rover, often at times of local sunrise or (as here) sunset. (Part of one wheel is visible at lower right.)
NASA description: This image was taken by Mars Descent Imager (MARDI) onboard NASA’s Mars rover Curiosity on Sol 597 (2014-04-11 18:08:40 UTC).
More Sol 597 images (from all cameras), and Curiosity’s latest location map.