Most computer scientists could rattle off their powers of 2 just as easily as their powers of 10.

Unfortunately in this instance, Daniel has discovered that possessing such "power"ful knowledge could prove dangerous when it comes to validation:

/*
=============
checkSize
Make sure the image is a power of 2.
=============
*/
int checkSize(int x) {
  if (x == 2 || x == 4 || x == 8 || x == 16 || x == 32 || x == 64 || x == 128 || x == 256 || x == 512)
    return 1;
  else
    return 0;
}

Apparently the original developer disregarded the infinite set of other numbers that are powers of two, along with the existence of the Boolean type.