function GetFormat(Filename: String): String;
 function IsPatten(Buffer: TBytes; Index: Integer; Values: array of Byte): Boolean;
 var
   I: Integer;
 begin
   Result := True;

   for I := Low(Values) to High(Values) do
     if Buffer[I+Index] <> Values[I] then
     begin
       Result := False;
       Break;
     end;
 end;
const
 CheckSize = 12;
var
 Stream: TFileStream;
 Buffer: TBytes;
 FileExt: String;
begin
 Result := '';

 try
   Stream := TFileStream.Create(FileName, fmOpenRead or fmShareDenyWrite);
   if Stream.Size > CheckSize then
   begin
     SetLength(Buffer, CheckSize);
     Stream.ReadBuffer(Buffer, CheckSize);

     if IsPatten(Buffer, 0, [$FF, $D8, $FF]) then Result := 'JPG'
     else if IsPatten(Buffer, 0, [$42, $4D]) then Result := 'BMP'
     else if IsPatten(Buffer, 0, [$47, $49, $46, $38]) then Result := 'GIF'
     else if IsPatten(Buffer, 8, [$57, $45, $42, $50]) then Result := 'WEBP'
     else if IsPatten(Buffer, 0, [$49, $20, $49]) then Result := 'TIFF'
     else if IsPatten(Buffer, 0, [$49, $49, $2A, $00]) then Result := 'TIFF'
     else if IsPatten(Buffer, 0, [$4D, $4D, $00, $2A]) then Result := 'TIFF'
     else if IsPatten(Buffer, 0, [$4D, $4D, $00, $2B]) then Result := 'TIFF'
     else if IsPatten(Buffer, 0, [$38, $42, $50, $53]) then Result := 'PSD'
     else if IsPatten(Buffer, 0, [$49, $49, $55, $00]) then Result := 'RAW'
     else if IsPatten(Buffer, 4, [$66, $74, $79, $70, $68, $65, $69, $63]) then Result := 'RAW'
     else if IsPatten(Buffer, 0, [$25, $50, $44, $46]) then Result := 'PDF'
     else if IsPatten(Buffer, 0, [$89, $50, $4E, $47, $0D, $0A, $1A, $0A]) then Result := 'PNG';
   end;
   Stream.Free;
 except
   on e: Exception do
   begin
   end;
 end;
end;