There are some white sponts in the top side(clearly visible in the right photo). Can anybody tell me the reason ? I think this is because of the dust particle. How can I avoid this. This is a semi SLR camera (Nikkon L120).
They appear to be marks on either your skylight filiter, or worse still, on the front element of your lens (assuming that you didn't have a filter on.) If you want to clean any lens or filter, be sure to use lens tissue !!
Otherwise you are almost certain to cause scratching
You can buy lens tissue at any decent camera shop
Oh, and use a blower-brush first - get rid of any dust that might be there. If dust or grime doesn't blow off, then breathe over the lens (or filter), and then very carefully and gently clean with a lens tissue. Then dispose of the lens tissue - never use one more than once.