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// For complete examples and data files, please go to https://github.com/groupdocsmetadata/GroupDocs_Metadata_NET

                    string path = Common.MapSourceFilePath(filePath);
                    // initialize GifFormat
                    GifFormat gifFormat = new GifFormat(Common.MapSourceFilePath(filePath));

                    // get image base64 string
                    string base64String;
                    using (Image image = Image.FromFile(path))
                    {
                        using (MemoryStream m = new MemoryStream())
                        {
                            image.Save(m, image.RawFormat);
                            byte[] imageBytes = m.ToArray();

                            // Convert byte[] to Base64 String
                            base64String = Convert.ToBase64String(imageBytes);
                        }
                    }

                    // create image thumbnail
                    Thumbnail thumbnail = new Thumbnail { ImageBase64 = base64String };

                    // initialize array and add thumbnail
                    Thumbnail[] thumbnails = new Thumbnail[1];
                    thumbnails[0] = thumbnail;

                    // update thumbnails property in XMP Basic schema
                    gifFormat.XmpValues.Schemes.XmpBasic.Thumbnails = thumbnails;

                    // commit changes
                    gifFormat.Save(Common.MapDestinationFilePath(filePath));