Encrypting an image

How can I encrypt an image?


procedure EncryptBMP(const BMP: TBitmap; Key: Integer);
var
BytesPorScan: Integer;
w, h: integer;
p: pByteArray;
begin
try
BytesPorScan := Abs(Integer(BMP.ScanLine[1]) -
Integer(BMP.ScanLine[0]));
except
raise Exception.Create('Error');
end;
RandSeed := Key;
for h := 0 to BMP.Height - 1 do
begin
P := BMP.ScanLine[h];
for w := 0 to BytesPorScan - 1 do
P^[w] := P^[w] xor Random(256);
end;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
EncryptBMP(Image1.Picture.Bitmap, 623);
Image1.Refresh;
end;

Call the function again to decrypt it