diesunddas on "Header: How to insert a non-clickable picture with two banners above?"

Theme: Twenty Fourteen
Homepage: redseabiodiversity.senckenberg.de

As you can see, the header of my homepage currently
contains a non-clickable picture.

Now I want to add two banners (centered, one left, one right)
beside the main heading with the fish. They should link
to the hp's of the project affiliates to be opened in a new
window. An example how it might look like is to be found here.

I am currently only able to generate the code for the banners.
One of them is like this:

<a href="Link goal" target="-blank"><img src="my image on the server" alt="KAU" width="200" height="153" class="aligncenter size-full wp-image-95" /></a>

But how and where to insert it into the header? And how to modify
the code snippet itself for to be placed in a layer above the basic
picture?

I have read about a z-value defining layers in wordpress but
I have no coding experience at all.

Though,I tried various things like visual editor-, header design-, and
other plugins, but nothing properly works.

So please be patient with me as a coding noob. I am sure
I can follow your instructions even if I have to modify
some php files.

Thank you and regards!