Hi,

When you click the "Insert Link" dialog, you would have to enter HTML into the dialog's Text field, for example:

<img src="https://www.google.com/images/srpr/logo3w.png" />

It will insert Google's logo as the link image. You can customize the dialog to let user only enter image Url and automatically creates the above HTML based on the Url entered. You can find more information on how to customize the dialog here:

http://www.essentialobjects.com/doc/1/editor/customize_dialog.aspx

Thanks!