Entropy = 7.980627 bits per character.

The information density of the contents of the file, expressed as 
a number of bits per character. The results above, which resulted from 
processing an image file compressed with JPEG, indicate that 
the file is extremely dense in information--essentially random. 

Hence, compression of the file is unlikely to reduce its size. 

By contrast, the source code of the program has entropy of about 4.9 
bits per character, indicating that optimal compression of the file
would reduce its size by 38%. 

http://www.fourmilab.ch/random/