How To change Background pic of my Header Web Page , for batter i have attached snapshoot  of my required change area of website.

Please help me  with brief description.

@Biswajit
Rightclick on item and click inspect, you can browse html elements and see background or background-color property, in which file and on what line it is.

ok , I have check your as per your guidance, now can i implement a picture on that area 'id="header-search".

Please help me .

you can try through style... something like that.

#header-search {float:left;width:100%;clear:both;background:#fff;padding:25px 0;position:relative;z-index:8;background: url(../images/wallperz.jpg) no-repeat center center fixed;}

which file need to modify in my Veronika theme, tell me the filename where need to modify