uses
 Jpeg, ClipBrd;

procedure TfrmMain.ConvertBMP2JPEG;
// converts a bitmap, the graphic of a TChart for example, to a jpeg
var
 jpgImg: TJPEGImage;
begin
 // copy bitmap to clipboard
 chrtOutputSingle.CopyToClipboardBitmap;
 // get clipboard and load it to Image1
 Image1.Picture.Bitmap.LoadFromClipboardFormat(cf_BitMap,
 ClipBoard.GetAsHandle(cf_Bitmap), 0);
 // create the jpeg-graphic
 jpgImg := TJPEGImage.Create;
 // assign the bitmap to the jpeg, this converts the bitmap
 jpgImg.Assign(Image1.Picture.Bitmap);
 // and save it to file
 jpgImg.SaveToFile('TChartExample.jpg');
end;