When an imaging session is completed or paused, it is possible to see its summary in the Imaging sessions summary page. Now there is also a possibility to export lists which would clearly indicate which of the sectors on the source drive have been successfully imaged, which have not (if any), and which of the sectors contained errors.
To export such list:
1) Click Image icon in the left-side menu and select the source drive
2) In the session summary, click the Export icon
3) Select the sectors you are interested in (e.g. Imaged sectors)
4) Save the downloaded .csv file
This file shows the ranges of imaged sectors: