I added some dirty pictures of Curiosity to Curiosity is still dirty! after August 9, 2018 (Sol 2137), and in this March 2021 selfie PIA24543: Curiosity's Selfie at Mont Mercou things still look roughly the same almost three years later.
There are some cropped bits below from the 21 MB JPEG downloadable there.
- Has Curiosity ever taken a good hard look at the dirt covering its top surface? The standard selfie-taking procedure probably tries to "stand back" for a wider view rather than zooming or moving in. Perhaps some spacecraft-health images have been taken at a closer distance with better resolution?
- Can it? Maybe not. I don't know the complete range of motion and depth of focus available to whatever ghostly arm does the selfie taking that we never get to see :-)
- Have individual particles been sized? In any image, has a single bit of Mars "dust" or regolith been large enough that it could be resolved in a photograph? Is there a record for the largest bit of dust that wind could bring aloft and redeposit on to Curiosity? Can MAHLI get up there and take a high magnification image of the dust?