Header Image will not display

Please see the attached link: Here I have tried to get the header image to display. It will display as soon as I select "enable feature" on "Homepage/frontpage". However, when I select any value from the "Page/Post Featured Header Image Size" drop down menu the header image goes away. Since it is not possible to reset that menu to a blank value the image never comes back. I tried uploading other images, but it's impossible to make it display. How can I fix this problem?