Opening the PNG file we see at the top left of the letter I a group of pixels in black an white. Understanding them as “black=1” and “white=0” we obtain:
  00110001001  10010001100  11001101000  01101010011  01100011011  10011100000
Concatenating them and deleting the last 2 zeros, we obtain  “0011000100110010001100110011010000110101001101100011011100111000” what converted to ASCII becomes “12345678”, so the flag is: INSA{1234578}
By: fikih888