There is a huge difference between image back-up and a database back-up. It's a long story to explain everything of a database back-up, so I suggest you first read articles/blogs to extend your knowledge (like: https://www.sqlservercentral.com/stairways/stairway-to-transaction-log-management-in-sql-server and https://www.sqlshack.com/understanding-sql-server-backup-types/ )
Short answer: it is NOT correct to only use image back-up.
- Images are like a snapshot and can only be used to revert to that single moment when the image was created. This type of back-up doesn't take database integrity into account and a revert could lead to a corrupt database. It will also NOT limit the size of the database LOG file, resulting in an ever increasing file and eventually a full disk.
- A good database back-up strategy can be used to revert the database to any moment in the past. Regular LOG back-ups are required for databases in FULL recovery model (as they are with Always On). This will keep LOG file size within limits.
** Don't mistake the ‘stupidity of the crowd’ for the ‘wisdom of the group’! **