Active or in-active pixels 
I have coloured dots showing on my image. What is it?  
These are active or in-active pixels.    
What are Pixels?  
Pixels are an item of information. They are arranged in a grid order using dots, squares or rectangles. Each pixel contains the information of the image you have taken.
Why is my image effected? 
All digital cameras have active or in-active pixels, it is impossible to produce a CCD with out them. These no-corporative pixels are turned off and a mapping file is produced to identify where they are. This mapping file is applied to every imager and lives with in your camera image processing circuit.  
Can the active or in-active pixels be removed? 
We can re-map the pixels using service software. CCD's can develop new naughty pixels and it is necessary to produce a new mapping file. Only a service center with the appropriate software can re-map a CCD. If the re-map fails a new CCD will be required.