Sending information back and forth between satellites and ground
tracking stations is accomplished by sending numerical codes.
Indeed, computers typically communicate using a BINARY SYSTEM of ones and zeros in combination.  For example, the number four in binary is 100 (zero is 0,
one is 1, two is 10, three is 11, four is 100, five 101, and so on). Using
such a scheme, any image can be transferred electronically by first using
an encoded message and second by putting that information into a
predetermined grid of rows (across) and columns.  One might transmit the
letter "T" over the telephone by saying, using a 3 X 3 grid and starting
in top left hand corner, and using a zero for white and a one for black as:          
 

1	1	1
0	1	0
0	1	0

      
In this way, images can be transported electronically.  The example above
used a 3 X 3 pixel image but you can easily imagine how much information
would have to be transported for a 256 X 256 grid (65,536 ones and zeros
including header information that describes the grid size and color
codes).  Electronic information is voluminous indeed!