Sometimes when you decide to share your event on Facebook, it may not have actively checked the page for your images or information.
This can be fixed by going to Facebook's Sharing Debugger page, from there click on the "Sharing Debugger" tab and entering the URL(The address found at the top of the browser, for example, "www.billetto.co.uk/e/1234") of your event and click the "Debug" button.
1. If your link is new, you might need to click the "Fetch new information" button to get Facebook to recognise the link.
2. If the image still doesn't appear, click the "Scrape again" button until the correct image appears.