Sichere Erkennung von PNG bzw. JPG?

[Redeemer]

In neueren Delphis haben die Grafikklassen das glaube ich selbst.

Ansonsten:

Delphi-Quellcode:

type TImageFormat = (unknown, BMP, GIF, JPG, PNG);

function GetImageFormat(Stream: TStream): TImageFormat;
var
  Memory: array[0..8] of Byte;
begin
  Result := unknown;

  try
    if Stream.Size < 10 then
    Exit;

    Stream.Position := 0;
    Stream.Read(Memory, 9);
    case Memory[0] of
      66: if Memory[1] = 77 then // BM: Bitmap
          Result := BMP;
      137: if Memory[1] = 80 then // ‰PNG: PNG
           if Memory[2] = 78 then
           if Memory[3] = 71 then
           if Memory[4] = 13 then
           if Memory[5] = 10 then
           if Memory[6] = 26 then
           if Memory[7] = 10 then
           Result := PNG;
      71: if Memory[1] = 73 then // GIF8...a
          if Memory[2] = 70 then
          if Memory[3] = 56 then
          if Memory[5] = 97 then
          case Memory[4] of
            55: Result := GIF; // 7: GIF, old
            57: Result := GIF; // 9: GIF, new
          end;
      255: if Memory[1] = 216 then // ÿØ: JPEG
           Result := JPG;
    end;
  except
  end;
  Stream.Position := 0;
end;

function LoadImageFromStream(Target: TPersistent; Stream: TStream): Boolean;
var
  GraphicClass: TGraphicClass;
  Graphic: TGraphic;
begin
  Result := False;
  case GetImageFormat(Stream) of
    BMP: GraphicClass := Graphics.TBitmap;
    PNG: GraphicClass := TPNGImage;
    JPG: GraphicClass := TJPEGImage;
    GIF: GraphicClass := TGIFImage;
    else raise EInvalidGraphic.CreateFmt(SInvalidImage, []);
  end;
  if not (GraphicClass = nil) then
  begin
    Graphic := GraphicClass.Create;
    try
      Graphic.LoadFromStream(Stream);
      Target.Assign(Graphic);
      Result := True;
    finally
      Graphic.Free;
    end;
  end;
end;