{1.image 2.'den büyük çözünürlükte olmamalı hata verir bunu try except ile 
runtime'da engelleyebilisiniz }
 
procedure TForm1.Button1Click(Sender: TObject);
var
 b1, b2: TBitmap;
 c1, c2: PByte;
 x, y, i,
 different: Integer;
 BytesPerPixel:longint;
begin
 b1 := Image1.Picture.Bitmap;
 b2 := Image2.Picture.Bitmap;
 Assert(b1.PixelFormat = b2.PixelFormat);
 different := 0;
for y := 0 to b1.Height - 1 do
begin
  c1 := b1.Scanline[y];
  c2 := b2.Scanline[y];
for x := 0 to b1.Width - 1 do
for i := 0 to BytesPerPixel - 1 do
begin
Inc(different, Integer(c1^ <> c2^));
Inc(c1); Inc(c2);
memo1.lines.add(inttostr(different));
end;
end;
end;