Add more then one site logo – custom-logo theme support

I think you might be looking for something like this:

add_theme_support( 'custom-logo', array(
    'height' => 480,
    'width'  => 720,
) );

You could also go with:

add_theme_support( 'custom-header', array(
    'height' => 480,
    'width'  => 720,
) );

Use the custom-header for the top logo and the custom-logo for the footer (or the other way round).

Another approach might be to define a thumbnail size:

 add_image_size( 'custom-footer-logo', 220, 220, array( 'left', 'top' ) );

You would have to work with the WordPress customizer controls to make a control to add and change the footer. But you could add as many images to your theme as you want that way.