Magento_Root/vendor/magento/module-catalog/Block/Product/View/Gallery.php

public function getGalleryImages()
    {
        $product = $this->getProduct();
        $images = $product->getMediaGalleryImages();
        if ($images instanceof MagentoFrameworkDataCollection) {
            foreach ($images as $image) {
                /* @var MagentoFrameworkDataObject $image */
                $image->setData(
                    'small_image_url',
                    $this->_imageHelper->init($product, 'product_page_image_small')
                        ->setImageFile($image->getFile())
                        ->getUrl()
                );
                $image->setData(
                    'medium_image_url',
                    $this->_imageHelper->init($product, 'product_page_image_medium')
                        ->constrainOnly(true)->keepAspectRatio(true)->keepFrame(false)
                        ->setImageFile($image->getFile())
                        ->getUrl()
                );
                $image->setData(
                    'large_image_url',
                    $this->_imageHelper->init($product, 'product_page_image_large')
                        ->constrainOnly(true)->keepAspectRatio(true)->keepFrame(false)
                        ->setImageFile($image->getFile())
                        ->getUrl()
                );

          / * Product Name to ImageName (Alt) */

                 $image->setData(
                    'img_alt',
                    $product->getName()
                );
            / * End Product Name to ImageName (Alt) */

            }
        }

        return $images;
    }

public function getGalleryImagesJson()
    {
        $imagesItems = [];
        foreach ($this->getGalleryImages() as $image) {

          / * add label to image name get */

             $label = ($image->getLabel()) ? $image->getLabel() : $image->getData("img_alt");

            $imagesItems[] = [
                'thumb' => $image->getData('small_image_url'),
                'img' => $image->getData('medium_image_url'),
                'full' => $image->getData('large_image_url'),
                'caption' => $label, // to pass the caption lable varible
                'position' => $image->getPosition(),
                'isMain' => $this->isMainImage($image),
            ];
        }
        return json_encode($imagesItems);
    }