I'd try to stay away from making direct database changes, it's too easy to miss something.
If you are going to delete, I'd stick to the API:
But I think a better solution, is to change the storage provider of the images.
You can use either the file system or some kind of CDN host like Amazon. This will free up space in the database, and if you store the images remotely, you'll lessen your server burden a bit.