You will probably have to make customizations to your theme files, and place the search PHP shortcode there. I would only recommend doing this if you have a good experience with PHP, HTPL and CSS programming. There is unfortunately to exact way of doing this, as every theme is different.
Another possibility is to maybe use a live editor like Visual Composer or Live Composer if you want to place it on an image.
On the demo I use visual composer to create full width modules and use background images to the content.Best,
If you like my products, don't forget to rate them on codecanyon :)