In running some checks against my site I got an error alter like this:
The page with URL "http://www.domain.com/images/main/276/?C=D;O=D" can also be accessed by using URL "http://www.domain.com/images/main/276/?C=N;O=D".
Search engines identify unique pages by using URLs. When a single page can be accessed by using any one of multiple URLs, a search engine assumes that there are multiple unique pages. Use a single URL to reference a page to prevent dilution of page relevance. You can prevent dilution by following a standard URL format.
What is this ?C=D;O=D stuff?
These are directories that hold images.