In one of the posts, it was mentioned the following:
Save and upload the ini file, go to your EzPublish content edit interface, choose an image (the 'back' one you made earlier) choose the mypicturewitharoundedborder alias from the dropdown and publish. When you are happy that it's working delete the 'front' image and replace it with one that does something useful!
I apologise. I just meant the online editor. Once you have added the mask file, the filters and the alias entry in the image.ini.override file adding an image with rounded borders is as simple as selecting it from the available image classes in the 'Insert Object' popup. Adding the alias (AKA image_class) to the ini file is what makes it available. To make life interesting the alias/image_class is called 'size' in the box.