Resize images

      i have to resize the slider images to the right measurements, because my customer has problems with editing images.
      I have an upload form, where i can upload all my images and some file pickers where i can select the needed slider image.
      If i do it with the .media page object it works fine, but i have to loop true the in the Admin Panel selected slider 
      images and resize them.

      That is my .md file

      ```
      slider:
          -
              sliderbild: slide1.jpg
          -
              sliderbild: slide2.jpg
          -
              sliderbild: slide3.jpg

      bilder:
          user/themes/hotel/assets/images/home/slide2.jpg:
              name: slide2.jpg 
              type: image/jpeg
              size: 340748
              path: user/themes/hotel/assets/images/home/slide2.jpg
          user/themes/hotel-fontanella/assets/images/home/slide1.jpg:
              name: slide1.jpg
              type: image/jpeg
              size: 374014
              path: user/themes/hotel/assets/images/home/slide1.jpg
          user/themes/hotel-fontanella/assets/images/home/slide3.jpg:
              name: slide3.jpg
              type: image/jpeg
              size: 348107
              path: user/themes/hotel/assets/images/hhome/slide3.jpg      
      permalink: home
      ```

      That is my twig code: 

      {% for item in page.header.slider %}
        <div><img src="{{ url("theme://assets/images") }}/{{ header.permalink }}/{{ item.sliderbild }}" alt="Hotel Fontanella" /></div>
      {% endfor %}

      How can i resize the images without the .media object?
      Any ideas?

      Best regards