Used sizes?

Hello,

Plugin will not remove those images since it has no way of detecting their request (it only detects images that are called using one of the WordPress internal functions for fetching attachments). The plugin never removes sizes that you can choose from when inserting an image inside the post, including ‘thumbnail’, ‘medium’ and ‘large’: https://github.com/OriginalEXE/Optimize-Images-Resizing/blob/master/inc/class-cli-command.php#L87
I would still recommend creating a backup of your website just in case something goes wrong, you can never be too safe.