The image source that is used will come from combining the Root URL and the relative path to the images folder. If the images folder is in the root of your site then you should be able to specify it without any preceding slashes.
Here is an example of this:
If the images folder is at cmsImg/ then you should be able to use this value for the images path:
This should work for you if your Root URL path is set to www.mydomain.co.uk/.