Hello,

you can't manage images for news using the gnews sitemap. The Google News XML format doesn't support images informations at all. What image to pick for the news is up to Google based on the HTML of your website, the only way that you could help Google to identify a particular image is using meta tags for medias.

Said that, i've no idea how and why Google is showing a link to the image not good in the search result, but most probably it's related only on informations found in the HTML by the Google Bot, nothing to do with sitemaps.