i want to get the "post covers" from easyblog in the image sitemap. i have tried over hours to get this to work.

example what images i mean (the only image in this post): http://easyblog.stackideas.com/joomla-3-5-updates

in this blog post you see a cover image, exactly this images i want to grab for the sitemap from all my blog posts. how do i do that?

Because that's not an image ( real <img> tag ), it's an anchor tag ( <a> ) with applied a CSS image as a background.
To allow the images crawler to recognize and grab it you can try to enable the parameter 'Recognize galleries images' in the JSitemap configuration. Obviously ensure that the images sitemap that you are generating includes the easyblog links, you may need the precaching if you have many links.

on my site all blogs have a cover image. it is the representative (eye catcher) look for the blog contend. the rest of the images i don't care in the blogs. i thought about this what would the best for the content of the sitemap and the speed of generating all images (i use a cronjob once a day for my image sitemap).
i came to the conclusion that i do not need any image in the blog content except the covers, how can i do this without your first idea of the "Recognize galleries images" because i only need the covers?

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.

ok i understand.
this setting "Recognize galleries images" is in the configuration, this means it get turned on in all sources. is it possible to make this optional in each sources instead?
i need this only in the "Easyblog" source.

No that's a configuration settings that applies globally, but you don't even need to apply it to a single data source.
Each data source can be excluded from the images sitemap, so you can leave only active the one of Easyblog, moreover using the inclusion filters you can specify a path to match only the Easyblog image of your interest .