Hi,
thank you very much for answering AND giving an idea.
Without rewriting the template it must be possible:
1) just create a new categroy (e.g. slider-images) for blog posts,
2) write for example 4 blank posts without any content but with your favorit image as blog post image,
3) select the new category slider-images for this new blog post
4) Save this blog, select in the overview of blog posts QuickEdit for our new blog post and change the date to an early date of your blog posts.
5) select in Theme options -> “Which category to pull from” the new categroy
Now, only the images of the category slider-images will be shown, but the blank posts are not invisible because of their date.
Sorry for my bad english. Hope you understand ist.
Sincerly,
Uwe