Actually a casual observer can distinguish ECB from random, though they may not realize that is what they are doing. For example if you manage to compress the

Actually a casual observer can distinguish ECB from random, though they may not realize that is what they are doing. For example if you manage to compress the ciphertext -- random data should not compress by much so if you can do any significant compression on ciphertext then you are distinguishing it from random bits. ECB should be compressable if the plaintext is compressable (though probably not as well as the plaintext do to the way ECB is divided into blocks). Recognizing that this is a problem is another matter.