I have a document in which I have inserted a picture as the header. It is a banner. In print preview, the picture is placed on the edge of the page. There is no space on the top or on the left side of the page, but on printing there is 1 inch gap on the top and 1/2 gap on the left side of the paper from the picture. How can avoid this ? In "page setup" I have given "Top" as "0".
Most consumer-level printers cannot print right to the edge (aka Full Bleed).
In most cases you'll need a printer that can print a larger page than you want to use, and then you design and print it as if it's on the larger size paper, but then force it to print to the smaller paper size. Even then, the leading edge (the top edge usually) border is tough to deal with, as many printers need the border edge to grab and hold the page while the printing is happening.
Often professional (digital) print shops will accomplish Bleeds by just printing to the larger size paper and then trimming/cutting the pages down to the size they want, eliminating any empty margins (perhaps check out What are crop marks and why would you want to print them?).