The insert image buttom in the WYSIWYG should be configured so as to allow users to select images from uploaded files. The selection populates the Image URL and serves as a shortcut for the user.
It does include the images that are uploaded to the page, but not the images uploaded to the theme. The problem with including theme images is that you could change the theme and then those images wouldn't work anymore.
Julie Niemi tagged this with Website 2013-06-10 15:15:00 -0700
Jim Gilliam responded 2011-08-02 12:15:04 -0700
Jerimee Richir commented 2011-08-02 11:43:21 -0700Oh it looks like it does do this for files associated with the content item. My suggestion is that it should also look in the library of files uploaded to the theme.