This question has been answered by sottwell. See the first response.
<base href="[[!++site_url]]" />
There's nothing fancy about images within MODX, if the path is correct. After adding a base href:Thanks,I got it inserted,now I only need to it be responsive like my logo..it's size is adjusted to the screen size and it always stays in the middle of the page..whereas the image I inserted stays a fixed size.Instead of filling up the whole top of the page the right hand side is empty as the image doesn't reach.
<base href="[[!++site_url]]">
to your head, your paths can look like /assets/folder/filename.jpg and still resolve to http://yourDomain.com/assets/folder/filename.jpg
A bit of code would help us help you, for sure.
max-width: 100%;