How to use a barcode scanner to recognize the front and back of a barcode? Can it be recognized?

Regardless of the positive and negative direct use of the scanner can scan the results, there is no need to distinguish between positive and negative. The specific coding rules I read a long time ago have forgotten, it should be the bar code has a special indication of the direction of the code bit. So if you want to go to the point, you can check the coding rules and then find out the coding bits that represent the positive and negative to deduce the positive and negative is also possible.