Append binary data for image datatype in SQL server

First, as others have said, you should use VARBINARY type instead of IMAGE.

Anyway, if you still want to use IMAGE, you can use UPDATETEXT command like this:

DECLARE @Pointer VARBINARY(1);
SELECT @Pointer = TEXTPTR(Data) FROM TableName WHERE Id = @Id;

UPDATETEXT TableName.Data @Pointer @Offset @Delete WITH LOG @Bytes;

Consider:

@Bytes = the actual bytes you want to append

@Delete = if you want to delete what it may have in its bytes positions

//Create Binary Data Stream  
    string filePath = Server.MapPath("APP_DATA/TestDoc.docx");
    string filename = Path.GetFileName(filePath);
    FileStream fs = new FileStream(filePath, FileMode.Open, FileAccess.Read);
    BinaryReader br = new BinaryReader(fs);
    Byte[] bytes = br.ReadBytes((Int32)fs.Length);
    br.Close();
    fs.Close();

--------------------
//insert the file into database

string strQuery = "insert into tblFiles(Name, ContentType, Data) values (@Name, @ContentType, @Data)";
SqlCommand cmd = new SqlCommand(strQuery,conn);
cmd.Parameters.Add("@Name", SqlDbType.VarChar).Value = filename;
cmd.Parameters.Add("@ContentType", SqlDbType.VarChar).Value = "application/vnd.ms-word";
cmd.Parameters.Add("@Data", SqlDbType.Binary).Value = bytes;
cmd.ExecuteNonQuery();

Note: ntext, text, and image data types will be removed in a future version of Microsoft SQL Server. Avoid using these data types in new development work, and plan to modify applications that currently use them. Use nvarchar(max), varchar(max), and varbinary(max) instead.