Maybe i wasn't enough self explaining, i try again. The cover image of easyblog is not an image, it's a anchor tag with applied a background using CSS. The only way to have it considered as an image for the sitemap crawler is activating the option "Recognize galleries images". That considers anchor tags linking to an image as a real image, even if it's not an image. Using filters for inclusions/exclusions you can setup the configuration to include only that 'image' and discard others, this is the standard behavior despite the option "Recognize galleries images" and this is how things work.