Official comment
Yes, there is an image manager, but at this time you can only access it through the "Add Image" function inside of an email or landing page editor in ONTRAPORT. In ONTRApages, ONTRAforms and ONTRAmail it is available as soon as you press the "Change Image" button:

In the older HTML Email editor it is two clicks away. After clicking the insert image icon, click on the "Select Hosted Image" button to access the image manager:

The image manager uses image Tags to organize the images. You can also display them sorted by upload date, name, type or size. The search function searches the names of the images.
