Is there any way not to use the Drupal Image-style system?
The Drupal image style system let you upload an image in whatever form you choose, and the image style will transform it into the size, shape, etc. of the selected style according to preset rules that you find in the configuration for image styles.

One of the benefits of the Image style system is that it allows reuse of images in different styles.  You just upload the image once, and than you can use a thumbnail size version in the teaser, and a large size in the main article - or two different styles of the same image in two different nodes, etc.

There is one folder per style (I believe there are 4 default styles, but you can create and add your own styles if you want to, and this will add more folders below the styles directory).

Drupal does not create a copy of the image for a particular style until that style is requested.  While there are 4 folders, if you don't reuse an image, it will only be created in one style - meaning that there will be two copies of that image on your disk: The original, and the scaled, cropped, whatever, copy that Drupal has created for that style.

In other words, you need to condsider the (IMHO) substantial benefits of Drypal's image style system before you decide to get rid of it.

But if you don't want to use it, you can do without.

However it is a bit more involved than just removing the image style folder.

Basically, what you do is to resize, crop, etc. the image yourself, before you upload it to the site.  Then you create (by hand) a link to the original that you've uploaded from whereever you want to use it.  If you do this with all images, Drupal will never attempt to create a copy for a particular image style and the image style folder will be empty.

If you're sure you're never is going to allow Drupal to style an image, I suppose you can remove the image style folder at this point, but I would leave the empty folder it in place to avoid breaking the site if I at some point forget that I'm not supposed to use Drupal's image styles.

If you think that a lot of unused copies of images are living below the image styles folder, you can flush all (or a subset) with the following Drush CLI command:

drush image-flush


This leaves the file structure below the image styles folder in place, so if a flushed image is requested, it will automatically be recreated in the requested style.