I don’t think you would need an option for this. The reason you are seeing the image in the blog loop is because I have set the default option to look for attachment files and make them the thumbnails automagically which is probably not a great idea.
With the below change I am suggesting, you won’t see an “featured” image for the post if you have not set the image as the featured image ( it should not be set if you do not plan to use it as one). Pls change the file framework/extensions/get-the-image.php file at line number 55 from
'attachment' => true,
to
'attachment' => false,
Hope this works for you. I have made sure this change will be part of next update and hence no need to worry about next update overwriting your change. Thanks.