Insert Image Into Posts Page

I have a blog page integrated into my website. I created a page (“blog”) and then went to Settings –> Reading –> Posts Page and set this to “blog.”

However, I need to add an image to this page and am having trouble doing so as once I set “blog” to “Posts Page” in settings, I cannot add an image to it.

I would like the person who clicks on the blog page see an image under the menu rather than first seeing the posts.

I am using Catch Base Pro by Catch Themes.