I've forgotten how to add images to glossaries ...
Should this be done via a URL?
Can't the image be displayed in the glossary pane?
Or with a file:/// URL for locally stored images.
If a Reference column name is set (Default: Reference) in Preferences > Definitions (maybe yours is "Image"), you can add a file at the new term creation to the glossary.
Click the Reference (or renamed) column button, and choose a file via the file chooser. You can also add a URL in the text field.
Is this what you were asking? From the screenshots, it seems like you got it figured out.
Displaying an image without opening it with an external program would be nice.