This extension worked perfectly until recently. Google must've changed something on the search page, because the direct link to the image no longer shows up at the bottom of the preview. Please update and fix.
This wallpaper is for an old version of Opera. See https://forums.opera.com/topic/35558/solved-some-wallpapers-are-not-really-added-resp-are-zip-files for how to make it compatible for modern, Chromium-based Opera.
This wallpaper is for an old version of Opera. See https://forums.opera.com/topic/37038/wallpaper-shows-as-installed-but-it-s-not for how to fix its persona.ini file to work with modern, Chromium-based Opera version. In short, look at the personi.ini of a wallpaper that works for how to fix this wallpaper's persona.ini. Or, just extract the zip file, get the image file out of it, click "add your wallpaper" in Easy-Setup in Opera and point it to the image file.