Ok, it seem that you are correct! Images are saved if a droplet is destroyed.

I found this at https://www.digitalocean.com/community/tutorials/digitalocean-backups-and-snapshots-explained:

“Occasional Usage: Snapshots can also provide a way to use droplets for a limited time without having to pay for hours when the server is not in use. Should you only need to use a server for a certain time every so often, you can take a snapshot of your current configuration, delete the droplet, and spin the system back up as soon as you need it once again—the image will remain in your account. In such a way, you only have to pay for the amount of time that you will actually use the droplet each month.”

And according to this article, How To Migrate Droplets Using Snapshots: https://cloud.digitalocean.com/support/suggestions?query=destroy%20droplet%20snapshot

The first sentence suggests otherwise:

“To migrate your server, take a snapshot of your server using the DigitalOcean snapshot tool, delete the original droplet, and spin up a new server from the snapshot.”