How do I add images to custom theme

I need to add an extra, static image in the page header. Right after the logo.

My child theme directory structure in
[magento project root]/app/design/frontend/My_Vendor/My_Theme/

  ├── Magento_Theme
  │   └── templates
  │       └── html
  │           └── header
  │               └── logo.phtml
  │               
  ├── media
  │   └── preview.png
  ├── registration.php
  ├── theme.xml
  └── web
      └── images
          ├── logo.png
          └── CUSTOM_TAGLINE.png

The CUSTOM_TAGLINE.png is missing in the static files, the rest works fine.

The symlinks to images are being generated in a static folder [magento project root]/pub/static/frontend/My_Vendor/My_Theme/my_language/images/. My custom logo.png appears there along with loader-1.gif which I assume comes from the parent theme. Unfortunately my custom image CUSTOM_TAGLINE.png is not there.

In my modified Magento_Theme/templates/html/header/logo.phtml I have the line echo $block->getViewFileUrl('images/CUSTOM_TAGLINE.png') that also works as expected, printing the path to the generated static folder.

What do I miss here? Do I need to declare the CUSTOM_TAGLINE.png somehow?