以下的程式碼，在98及2000皆可使用，但在XP無法使用，只要能偵測BMP及JPG即可，謝謝! 

function TForm1.PhysicalResolveFileType(Filename: string): Integer;
var
  p: PChar;
  AStream : TFileStream;
begin
  AStream := TFileStream.Create(Filename, fmOpenRead OR fmShareDenyNone);
  try
      Result := 0;
      if not Assigned(AStream) then
        Exit;
      GetMem(p, 10);
      try
        AStream.Position := 0;
        AStream.Read(p[0], 10);
        {bitmap format 1}
        if (p[0] = #66) and (p[1] = #77) then
          Result := 1;
        {tiff format 2}
        if ((p[0] = #73) and (p[1] = #73) and (p[2] = #42) and (p[3] = #0)) or
            (( p[0] = #77) and (p[1] = #77) and (p[2] = #42) and ( p[3] = #0)) then
          Result := 2;
        {jpg format 3}
        if (p[6] = #74) and (p[7] = #70) and (p[8] = #73) and (p[9] = #70) then
          Result := 3;
        {png format 4}
        if (p[0] = #137) and (p[1] = #80) and (p[2] = #78) and (p[3] = #71) and
            (p[4] = #13) and (p[5] = #10) and (p[6] = #26) and (p[7] = #10) then
          Result := 4;
        {dcx format 5}
        if (p[0] = #177) and (p[1] = #104) and (p[2] = #222) and (p[3] = #58) then
          Result := 5;
        {pcx format 6}
        if p[0] = #10 then
          Result := 6;
        {emf format 7}
        if (p[0] = #215) and (p[1] = #205) and (p[2] = #198) and (p[3] = #154) then
          Result := 7;
        {emf format}
        if (p[0] = #1) and (p[1] = #0) and (p[2] = #0) and (p[3] = #0) then
          Result := 7;
      finally
        Freemem( p );
      end;      FINALLY
      AStream.Free
  END;
end;
 

努力會更接近成功

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努力會更接近成功

只是判斷檔案內容中的檔頭格式，應該跟作業系統無關吧！

謝謝您的回應，，主因是我出外工作的編譯環境只有2000和98下程式可以使用，但前日至台北時在XP HOME SP2環境下卻出現偶而有作用，(162個檔約2-3O個檔有作用，很怪)和JPEG2000有關嗎??   以下是我今天到台中公司用xp(可能是PERFINAL版，沒注意是否為SP2)測的程式，可以使用

 
// Avoid JPEG Error #52:
  // Verify first two bytes of JPEG are $FFD8 (little endian $D8FF)
  // Verify last two bytes of JPEG are $FFD9 (little endian $D9FF)
  FUNCTION JPEGSentinelsAreOK(CONST Filename:  TFilename):  BOOLEAN;
    VAR
      FileStream:  TFileStream;
      w1        :  WORD;     // a "word" is always 2 bytes long
      w2        :  WORD;
  BEGIN
    ASSERT(SizeOf(WORD) = 2);        RESULT := FileExists(Filename);        IF   RESULT
    THEN BEGIN
      FileStream := TFileStream.Create(Filename, fmOpenRead OR fmShareDenyNone);
      TRY
        FileStream.Seek(0, soFromBeginning); // use seek or position
        FileStream.Read(w1,2);            FileStream.Position := FileStream.Size - 2;
        FileStream.Read(w2,2)
      FINALLY
        FileStream.Free
      END;          RESULT := (w1 = $D8FF) AND (w2 = $D9FF);
    END
  END;    

JPEG格式算可以用了 不知有沒有BMP格式的函數可以用，謝謝 努力會更接近成功

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努力會更接近成功

可能是檔案格式沒有比對完全。 1.BMP 檔案開頭 絕對應是 42 4D 開始。 2.JPG 為 FF D8 可以參考這裡 http://www.fastgraph.com/help/image_file_header_formats.html

謝謝您的回答 BMP的檔頭在此 

 
function GetBitmapDimension(const AFilename: String;
                            var AWidth, AHeight: Integer): Boolean;
var
  f : TFileStream;
  bfh : TBitmapFileHeader;
  HeaderSize : DWord;
  w : Word;
begin
  Result := False;
  AWidth := 0;
  AHeight := 0;
  f := TFileStream.Create(AFilename, fmOpenRead or fmShareDenyNone);
  try
    f.ReadBuffer(bfh, SizeOf(bfh));
    if bfh.bfType <> $4d42 then Exit;  // 'BM'
    f.ReadBuffer(HeaderSize, SizeOf(HeaderSize));
    case HeaderSize of
      SizeOf(TBitmapCoreHeader) : begin  // OS/2 Bitmap
        f.ReadBuffer(w, SizeOf(w));
        AWidth := w;
        f.ReadBuffer(w, SizeOf(w));
        AHeight := w;
      end;
      SizeOf(TBitmapInfoHeader),
      SizeOf(TBitmapV4Header),
      SizeOf(TBitmapV5Header) : begin
        f.ReadBuffer(AWidth, SizeOf(AWidth));
        f.ReadBuffer(AHeight, SizeOf(AHeight));
      end;
    else
      Exit;  // unknown Bitmap format
    end;
    // there are top down bitmaps with a negative height
    AHeight := Abs(AHeight);
    Result := True;
  finally
    f.Free;
  end;
end;    

努力會更接近成功

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努力會更接近成功