Default image by URL instead of ID?

Hello uwi,

This can be done. I’ve produced example code below. It will need tweak it to your needs.
Mainly the exceptions, you probably need conditionals?

function dfi_add_class($html, $post_id, $default_thumbnail_id, $size, $attr) {
    if ( 1==1 ) // add your exception logic here
    {
        return '<img src="https://www.your-domain.com/wp-content/uploads/xyz.jpg" class="add-your-own"/>';
    }
    // return the normal default featured image with it's html
    return $html;
}
add_filter( 'dfi_thumbnail_html', 'dfi_add_class', 10, 5 );

Wow – it works – thanks a lot! Nearby: What′s the meaning of “1==1”??

It’s just a test.

To read it in human language:

if ( 1==1 ) {
if one equals one then do
This is always true ??

You need to replace it with your own logic

Pffft… ok – got it! Thanks ??