BaseController.cs

        public virtual Tuple<string, string> GetAdaptiveImageUrls(Item item, string imageFieldName, int maxWidth = 300)
        {
            Assert.IsNotNull(item, nameof(item));
            Assert.IsNotNullOrEmpty(imageFieldName, nameof(imageFieldName));

            ImageField imageField = item.Fields[imageFieldName];
            if (imageField?.MediaItem != null /*&& imageField.MediaItem.Versions.Count > 0*/)
            {
                string imageUrl = HashingUtils.ProtectAssetUrl(MediaManager.GetMediaUrl(imageField.MediaItem, new MediaUrlOptions {MaxWidth = maxWidth}));

                // ReSharper disable once UseObjectOrCollectionInitializer
                var urls = new List<string>();
                urls.Add(HashingUtils.ProtectAssetUrl(MediaManager.GetMediaUrl(imageField.MediaItem, new MediaUrlOptions {MaxWidth = 100})) + " 100w");
                urls.Add(HashingUtils.ProtectAssetUrl(MediaManager.GetMediaUrl(imageField.MediaItem, new MediaUrlOptions {MaxWidth = 200})) + " 200w");
                urls.Add(HashingUtils.ProtectAssetUrl(MediaManager.GetMediaUrl(imageField.MediaItem, new MediaUrlOptions {MaxWidth = 300})) + " 300w");
                urls.Add(HashingUtils.ProtectAssetUrl(MediaManager.GetMediaUrl(imageField.MediaItem, new MediaUrlOptions {MaxWidth = 400})) + " 400w");
                urls.Add(HashingUtils.ProtectAssetUrl(MediaManager.GetMediaUrl(imageField.MediaItem, new MediaUrlOptions {MaxWidth = 500})) + " 500w");
                urls.Add(HashingUtils.ProtectAssetUrl(MediaManager.GetMediaUrl(imageField.MediaItem, new MediaUrlOptions {MaxWidth = 600})) + " 600w");
                urls.Add(HashingUtils.ProtectAssetUrl(MediaManager.GetMediaUrl(imageField.MediaItem, new MediaUrlOptions {MaxWidth = 1150})) + " 1150w");
                urls.Add(HashingUtils.ProtectAssetUrl(MediaManager.GetMediaUrl(imageField.MediaItem, new MediaUrlOptions {MaxWidth = 1290})) + " 1290w");
                urls.Add(HashingUtils.ProtectAssetUrl(MediaManager.GetMediaUrl(imageField.MediaItem, new MediaUrlOptions {MaxWidth = 1440})) + " 1440w");
                urls.Add(HashingUtils.ProtectAssetUrl(MediaManager.GetMediaUrl(imageField.MediaItem, new MediaUrlOptions {MaxWidth = 1920})) + " 1920w");

                return new Tuple<string, string>(imageUrl, string.Join(",", urls));
            }

            return new Tuple<string, string>("#", "#");
        }