<img src="<%# ResolveUrl("~/Pages/ImageDB.ashx?id="+Eval("Код")) %>" />

using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
using System.Web.Configuration;
using System.Web.Routing;

namespace Gidro.Pages
{
    
    public class ImageDB : IHttpHandler
    {

        public void ProcessRequest(HttpContext context)
        {
            string id = context.Request.QueryString["id"];
            if (id == null) throw new ApplicationException("Должен быть указан код");

            string strcon = WebConfigurationManager.ConnectionStrings["Gidro"].ConnectionString;
            SqlConnection con = new SqlConnection(strcon);
            string sql = "SELECT ОсновноеИзображение FROM Products WHERE Код = @Код";
            SqlCommand cmd = new SqlCommand(sql, con);
            cmd.Parameters.AddWithValue("@Код", id);
            try
            {
                con.Open();
                SqlDataReader r = cmd.ExecuteReader(System.Data.CommandBehavior.SequentialAccess);
                if (r.Read())
                {
                    int bufferSize = 100;
                    byte[] bytes = new byte[bufferSize];
                    long bytesRead;
                    long readFrom = 0;
                    do
                    {
                        bytesRead = r.GetBytes(0, readFrom, bytes, 0, bufferSize);
                        context.Response.BinaryWrite(bytes);
                        context.Response.ContentType = "image/png";
                        readFrom += bufferSize;

                    } while (bytesRead == bufferSize);
                }
                r.Close();
            }
            finally
            {
                con.Close();
            }
        }

        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }
}

        private string prefix = "testprovider.axd";
        public async Task<byte[]> GetImage(object id)
        {
            byte[] buffer = new byte[4096];
            if (id == null) throw new ApplicationException("Должен быть указан код");
            id = 494;//для теста указываю фиксировано, точно есть в базе
            string strcon = WebConfigurationManager.ConnectionStrings["Gidro"].ConnectionString;
            SqlConnection con = new SqlConnection(strcon);
            string sql = "SELECT ОсновноеИзображение FROM Products WHERE Код = @Код";
            SqlCommand cmd = new SqlCommand(sql, con);
            cmd.Parameters.AddWithValue("@Код", id);
            con.Open();
            using (SqlDataReader reader = await cmd.ExecuteReaderAsync())
            {
                if (await reader.ReadAsync())
                {
                    buffer = (byte[])reader["ОсновноеИзображение"];
                }
            }

            return buffer;
        }