Hi Monica
Navigate to the Attributes tab in the Query (Active should be numeric - 1 = Active, 2 = Inactive) and click on the Active attribute. In the Display Mappings section, change the drop-down from 'Color' to 'Icon'. Leave the Default Bucket row as-is. In the next row down, enter Green Checkmark in the Icon field (it should auto-complete), enter a Description (e.g. 'Active') in the Description field, and your From and To values should both be 1.
Then navigate to the Portlet and go to the Fields page of the List Column Section. Click through to the Properties page of your Active field and in the Display Elements section, tick the Image check-box and untick the Value checkbox.
You'll need to Publish the portlet for the changes to take effect for all users.