Comment by dmitrygr

   BigInt picToNumber(pic){
     BigInt x = 0;
     for (int r=0;r<pic.w;r++)
       for (int c=0;c<pic.h;c++)
         x = (x*265)+pic.pixel(r,c);

     return x;
   }

Yup...converts to number.. Unless they specify HOW, that means nothing. Anything is a number to a computer.