Would this be to select images or just to inspect images?
Would you want to be able to do some additional action with them?
Would you want all images used and unused, would that be a selectable option?
Would you like names or sizing info?
You probably already know this, but in Lectora Online if you click the Title Resources tab, a dialog comes up, and if you click the drop list and hover over the resource names you can see the resource’s thumbnail.