You can add an image of your own to an EpicTable map or tabletop using the "Image" button on the "Tabletops" tab.

This button will prompt you for an image file and will use that image as an object on the map or tabletop.  From there, you can move it around, resize it, whatever you need to do.  It's a great way to handle things that you need to throw onto the map on an ad-hoc basis.  For instance, if you need to add a bit of dungeon dressing or some rocks and trees.  

You can also just drag and drop images from Windows Explorer onto the tabletop.  I'll often have a folder of this kind of thing open so I can quickly grab whatever I need and drag it to the map.  (Copy-paste is not currently supported, but it's coming.)