pictures do not default from assets when editing site

[Provider7]

I have NetObjects Fusion 2015. I create a web site and use a picture from my desktop. After completing a page, I delete the picture. When I re-open the program to make changes on the page the picture does not display in the editor unless I restore the picture back on my desktop.

Why doesn't the program refer to the pictures in the asset folder where they are all located? Why does it go back to the source (desktop)?

Is there a way to get this to default to the asset folder?

Thanks in advance.