Refactored GetCoverImage to a static class and unit tested it. Enhanced the method by defaulting to folder.jpg file if exists, else takes first entry.

API/IO/ImageProvider.cs

@@ -0,0 +1,45 @@
+using System;
+using System.IO;
+using System.IO.Compression;
+using System.Linq;
+
+namespace API.IO
+{
+    public static class ImageProvider
+    {
+        /// <summary>
+        /// Generates byte array of cover image.
+        /// Given a path to a compressed file (zip, rar, cbz, cbr, etc), will ensure the first image is returned unless
+        /// a folder.extension exists in the root directory of the compressed file.
+        /// </summary>
+        /// <param name="filepath"></param>
+        /// <returns></returns>
+        public static byte[] GetCoverImage(string filepath)
+        {
+            if (!File.Exists(filepath) || !Parser.Parser.IsArchive(filepath)) return Array.Empty<byte>();
+
+            using ZipArchive archive = ZipFile.OpenRead(filepath);
+            if (archive.Entries.Count <= 0) return Array.Empty<byte>();
+
+            var folder = archive.Entries.SingleOrDefault(x => Path.GetFileNameWithoutExtension(x.Name).ToLower() == "folder");
+            var entry = archive.Entries[0];
+              
+            if (folder != null)
+            {
+                entry = folder;
+            }
+              
+            return ExtractEntryToImage(entry);
+        }
+
+        private static byte[] ExtractEntryToImage(ZipArchiveEntry entry)
+        {
+            var stream = entry.Open();
+            using var ms = new MemoryStream();
+            stream.CopyTo(ms);
+            var data = ms.ToArray();
+
+            return data;
+        }
+    }
+}