Theme thumbnail vs. reality

The thumbnail for this theme has that nice waterside town photo, but it’s just impossible to add an image in that photo’s place without hacking up the theme code. For a minute, I thought it was a widget area and I needed a slideshow plugin, but even that’s not the case– there’s only the sidebar widget area. What can I do to add an image in that place? I must be missing something, otherwise it wouldn’t be in the thumbnail, right?