var img : TMemoryStream;
    filename:string;
begin
 filename:=ExtractFilePath(Application.ExeName)+'/image.jpg';
 img:=TMemoryStream.Create;
 idHttp.Get('адрес картинки',img);
Image1.Picture.Graphic.LoadFromStream(img);
 {или  img.SaveToFile(filename);
 Image1.Picture.LoadFromFile(filename); }
 img.Free;