How can one put a 256 binary sequence or a 64 hexadecimal inside a 8x15 grid?

Assuming each grid can only fit 1 bit and only a max of 50 bits can be placed inside each cell of the grid?

padding & parity is allowed if needed
some form of conversion can be used after to convert the sequence

I found a bitcoin picture for sale a long time ago, inside of it was a yellow dot pattern that is not the eff xeros print pattern. I'm just trying to see if someone may have hid a private key in here.