Hello,
I created a new document of type File and uploaded a photo. Then, on the Properties -> Urls tab i set the following properties:
Document Url path: /abc
Url extensions : .jpg
and i checked the checkbox "Use custom url path".

Then on Home page I added an "editable image" webpart and I selected the image created previously.
If i access the image with <domain>/abc.jpg the image is displayed into the browser, so the .jpg extension works.
But the problem is that on the html source of the Home page, the link to the image uses .html extension instead of .jpg

Is this a bug or there is some other property (in cmssitemanager maybe?) that has to be set ?

Thank you