index.js

panel.plugin("medienbaecker/images", {
  fields: {
    images: {
      props: {
        label: String,
        buttons: String,
        value: String,
        images: Array
      },
      data() {
        return {
          test: "The files of the page",
          selected: []
        };
      },
      methods: {
        add(image) {
          this.selected.push(image);
          this.$refs.imageSelect.close();
        },
        remove(index) {
          this.selected.splice(index, 1);
        }
      },
      template: `
        <kirby-field :label="label" class="images">

          <kirby-button slot="options" icon="add" @click="$refs.imageSelect.open()">Select image</kirby-button>

          <kirby-draggable v-if="selected.length" element="kirby-list">
            <kirby-list-item
              v-for="(image, key) in selected"
              :key="key"
              :text="image.text"
              :image="image.image"
            >
              <kirby-button icon="cancel" slot="options" @click="remove(key)"></kirby-button>
            </kirby-list-item>
          </kirby-draggable>
          <kirby-box v-else text="Nothing selected"></kirby-box>

          <kirby-dialog ref="imageSelect">
            <kirby-list>
              <kirby-list-item
                v-for="(image, key) in images"
                :key="key"
                :text="image.text"
                :image="image.image"
              >
                <kirby-button icon="check" slot="options" @click="add(image)"></kirby-button>
              </kirby-list-item>
            </kirby-list>
          </kirby-dialog>

        </kirby-field>
      `
    }
  }
});

index.php

<?php

Kirby::plugin('medienbaecker/images', [
    'fields' => [
        'images' => [
            'computed' => [
                'images' => function () {
                    $images = [];

                    foreach ($this->model()->images() as $image) {
                        $images[] = [
                            'text'  => $image->filename(),
                            'image' => [
                                'url' => $image->url(),
                            ]
                        ];
                    }

                    return $images;
                }
            ]
        ]
    ]
]);