I'll assume you're using X theme, while that is outside the scope of support, I could point you in the right direction with the understanding that it would ultimately be your responsibility to take it from here.
Navigate to your parent theme's /x/framework/legacy/cranium/headers/views/global/ directory and copy the file _brand.php.
Then navigate to your child theme's /x-child/framework/legacy/cranium/headers/views/global/ directory and paste the file that you just copied. Then start modifying that file to place an image on the corners. You can use the html mark up below as your head start.
<div class="l-corner left">
<!-- This goes to the left corner -->
<div class="r-corner right">
<!-- This goes to the right corner -->