The sample shows how to support named streams with web API OData using some of the extensiblity points in the OData formatter.

NamedStreams.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using System.Web.Http.OData;
using System.Web.Http.OData.Builder;
using System.Web.Http.OData.Formatter;
using System.Web.Http.OData.Formatter.Deserialization;
using System.Web.Http.OData.Formatter.Serialization;
using Microsoft.Data.Edm;
using Microsoft.Data.OData;

namespace NamedStreams
{
    class Program
    {
        static void Main(string[] args)
        {
            HttpServer server = new HttpServer();
            server.Configuration.Routes.MapODataRoute("odata", "odata", GetEdmModel());

            server.Configuration.Formatters.InsertRange(0,
                ODataMediaTypeFormatters.Create(
                    new NamedStreamAwareSerializerProvider(), new DefaultODataDeserializerProvider()));

            HttpClient client = new HttpClient(server);

            PrintResponse("Get photos", client.GetAsync("http://localhost/odata/Photos").Result);
            PrintResponse("Get small image", client.GetAsync("http://localhost/odata/Photos(0)/SmallImg").Result);
        }

        private static void PrintResponse(string title, HttpResponseMessage response)
        {
            Console.WriteLine(title + "\n");
            response.EnsureSuccessStatusCode();
            Console.WriteLine(response.Content.ReadAsStringAsync().Result);
            Console.WriteLine(new String('*', 80));
        }

        private static IEdmModel GetEdmModel()
        {
            ODataConventionModelBuilder builder = new ODataConventionModelBuilder();
            builder.EntitySet<Photo>("Photos");
            return builder.GetEdmModel();
        }
    }

    public class Photo
    {
        public Photo()
        {
            Tags = new List<string>();
        }

        public int ID { get; set; }

        public ICollection<string> Tags { get; set; }

        public Stream SmallImg { get; set; }

        public Stream MediumImg { get; set; }

        public Stream LargeImg { get; set; }
    }

    public class PhotosController : ODataController
    {
        public IEnumerable<Photo> GetPhotos()
        {
            return new Photo[] { new Photo() };
        }

        public HttpResponseMessage GetSmallImg()
        {
            return new HttpResponseMessage
            {
                StatusCode = HttpStatusCode.OK,
                Content = new StringContent("....image stream01010010101001010....")
            };
        }
    }

    // custom serializer provider for using custom entity serializer.
    public class NamedStreamAwareSerializerProvider : DefaultODataSerializerProvider
    {
        private NamedStreamAwareEntityTypeSerializer _customEntitySerializer;

        public NamedStreamAwareSerializerProvider()
        {
            _customEntitySerializer = new NamedStreamAwareEntityTypeSerializer(this);
        }

        public override ODataEdmTypeSerializer GetEdmTypeSerializer(IEdmTypeReference edmType)
        {
            if (edmType.IsEntity())
            {
                // use our custom entity serializer.
                return _customEntitySerializer;
            }

            return base.GetEdmTypeSerializer(edmType);
        }
    }

    // custom entity type serializer that understands named streams.
    public class NamedStreamAwareEntityTypeSerializer : ODataEntityTypeSerializer
    {
        public NamedStreamAwareEntityTypeSerializer(ODataSerializerProvider serializerProvider)
            : base(serializerProvider)
        {
        }

        public override ODataProperty CreateStructuralProperty(IEdmStructuralProperty structuralProperty,
            EntityInstanceContext entityInstanceContext)
        {
            // if it is a named stream.
            if (structuralProperty.Type.IsStream())
            {
                return ToNamedStreamProperty(entityInstanceContext, structuralProperty);
            }

            return base.CreateStructuralProperty(structuralProperty, entityInstanceContext);
        }

        private static ODataProperty ToNamedStreamProperty(EntityInstanceContext entity, IEdmStructuralProperty streamProperty)
        {
            return new ODataProperty
            {
                Name = streamProperty.Name,
                Value = new ODataStreamReferenceValue
                {
                    ContentType = "img/png",
                    ReadLink = new Uri(entity.GenerateSelfLink(includeCast: false) + "/" + streamProperty.Name)
                }
            };
        }
    }
}