As per jccwrt – more sizes on flickr:
https://www.flickr.com/photos/132160802@N06/26912123620/sizes/o
Thanks to reddit and https://www.reddit.com/r/space/comments/4ktoha/curiosity_looks_back/
Curiosity Rover mission page on NASA’s website:
https://www.nasa.gov/mission_pages/msl/index.html