How can I remove random dots from an image?
OK, thanks to the fantastic Stack Exchange Ask a Question page, I have now a good idea of what they are and how to remove them. This is what I would describe as "pepper noise", as opposed to the traditional salt and peper noise. It can be removed by using a median filter, which essentially replaces each pixel by the median of the values of the pixels in some suitable neighbourhood around it. This is available directly in Photoshop, and as part of the Despeckle filter in the GIMP (see e.g. this resource). I hope this Q&amp;A will be useful for other people with the same problem.