Howdy Oran,
That’s a good question. Currently events have no default featured image, not from the organizer or the venue.
A year and a half ago someone suggested this feature, but unfortunately it has seen little user demand since. If you would like to see that option please vote on it (click here).
That said it would be very possible to write a customization which sets a default featured image. You could override the WP filter ‘tribe_event_featured_image’ with a custom image of your own choosing. Or using a theme override could just put the HTML for your image inside the actual template (checkout our Themer’s Guide for details on that if you’re interested). Both of these will require some WP theming knowhow though.
Does that answer your question? Please let me know. Cheers!
– Brook