I found PascalMagick - http://wiki.freepascal.org/PascalMagickBut project is very old (11+ years old), and it is not working for me.
procedure TForm1.ConvertToJPEG(Sender: TObject; FromFile: UTF8String; ToFile: UTF8String);var pic: TPicture; jpg: TJPEGImage;begin pic:=TPicture.Create; jpg:=TJPEGImage.Create; pic.LoadFromFile(FromFile); jpg.Assign(pic.Bitmap); jpg.CompressionQuality:=80; jpg.SaveToFile(ToFile); FreeAndNil(jpg); FreeAndNil(pic);end;