Now I have answer for this question so that I am writing here. By considering that it may be useful to others.
Basically this problem is from server side. If I become specific towards problem then its IP address blockage problem.
I transferred my web server source code from one server to other. Then after same above code worked perfectly and image gets uploaded without any problem.
So please before wasting any time, check your server side first because this kind of error definitely belong to server as per my understanding.
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