Hi there, Temin! Nice to see you again. 🙂
The closest way to get an image from an Additional Fields is to use a text field and paste the image in there as HTML. The fields accept HTML, so something like this would work:
<img src="[your-image-url]">
As an alternative, you can check out using a plugin like Advanced Custom Fields to create that functionality for you. Then you can modify the event template using a theme override to display the field. Â I highly recommend going this route if having the image upload feature is a must-have.
Cheers!
Geoff