We are working on a file browser plugin for this but we need "backend" support for that so we need to get the DEServer capabilities in place first, but that is another chapter.
This is rather straight forward but as all things "web/windows" it is not exactly as one imagine.
To use bad language, it is a proper bastard but in the original meaning of the word...
The HTMLEditor object is as the remainder of the app "native" to the app catalogue i.e. this means that the app catalogue is to be considered as ROOT.
So far so easy but here the bastard comes in, since the URL can be both a Web URL and a File URL HTMLEdit need some indication on how to read the url.
So if the image is stored in the App catalogue (good old DataEase tradition...) it should simply be to insert the name and off we go, but that is the trap. You need to tell it that it is a file and it want that by you telling it which drive we are on... C:
So if the image is called MyImage.PNG you need to write C:MyImage.PNG.
But after this it is easy. If it is stored in the sub-catalogue Images you simply write C:Images\MyImage.PNG and the rest is straight forward.