test.pas

function ToString(Stream:TMemoryStream):string;
begin
  Stream.Seek(0,0);
  SetString(Result, PChar(Stream.Memory), Stream.Size);
end;

procedure Main();
begin
  qry:=TQuery.Create(Props.ThreadSafeConnection);
  ms:=TMemoryStream.Create;
  bmp:=TBitmap.Create;
  try
    bmp.LoadFromFile('c:\somefile.bmp');
    bmp.SaveToStream(ms);
    ms.Seek(0,0);
    qry.SQL.Text:='update my_table set icon=:icon';
    qry.ParamByName('icon', true).AsBlob:=ToString(ms);
    qry.ExecSQL;
  finally
    qry.Free;
    ms.Free;
    bmp.Free;
  end;
end;