system.resizer.getAvailableSources

Triggered in System\Classes\ResizeImageItem.

Provides an opportunity to modify the available sources

Example usage:

Event::listen('system.resizer.getAvailableSources', function((array) &$sources)) {
    $sources['custom'] = [
         'disk' => 'custom',
         'root' => 'relative/path/on/disk',
         'url' => 'publicly/accessible/path',
    ];
});