[pablopessoa]

esto te va a servir :

Código Delphi [-]
procedure TForm1.guardarClick(Sender: TObject);
var
    jpg:TJPEGImage
    bmp:TBitmap;
begin
    bmp := TBitmap.Create;
    bmp.Width:= Image1.Width;
    bmp.Height:= Image1.Height;
    bmp.Canvas.CopyRect(Rect(0,0, bmp.Width, bmp.Height),        Image1.Canvas,Rect(0,0,Image1.Width,Image1.Height));
    //bmp.SetSize(640,480);
    jpg := TJPEGImage.Create;
    jpg.CompressionQuality := 100;
    jpg.Compress;    
    //asigna el bitmap al jpg, esto convierte el mapa de bit
    jpg.Assign(bmp); 
    jpg.SaveToFile('UnaRuta');
    jpg.Free;   
    bmp.Free;    
end;

Acordate de poner "Jpeg" en el uses del Form o no te va a compilar.
Saludos!!