After playing around with my new Nikon D90, I noticed that some of my dark pictures have a red spot near upper right corner. It turns out this is a “hot pixel”. Further research led me to the following interesting pages:
- http://www.shutterasia.com/forum/showthread.php?s=15d8e681214727cd9818820599fc1f45&t=24484
- pixelfixer - a tool for filtering out hot pixels from images
- good intro to hot pixels