Customise background image to display correctly on desktop pc and mobile devices

Hi, I am looking for an experienced web designer to customise my background image on my website so that it looks the same across all desktop web browsers, any monitor screen size, and mobile browsers. The problem I currently have is that when you view my website on a large monitor screen or on the mobile browser for example, the background image is either cut off on some parts or displaced. Another problem I have noticed is that when you resize the browser window on a pc, the background image doesn’t scale to the size of the window, and on a mobile browser majority of the image cannot be seen. I need the background image to keep its positioning and alignment regardless the web browser or computer/mobile device the end user will be using. If you have the skills and experience to do this job, I would love to hear from you.