A method for serializing products using a barcode and checking authenticity of barcodes. A printing modification introduces an authentication feature into the barcode. Print batch data comprising a batch of serial codes and an individual security rationale for modifying the barcode is provided. A modified barcode is printed using a single serial code out of the range of sequential serial numbers and the assigned individual security rationale to provide the barcode with an authentication feature. To check authenticity of a barcode, an image of the modified barcode is processed and submitted to a central database. Content of the modified barcode is read to decode the serial number. The serial number is used to identify a print batch and individual security rationale. If reconstructed properties of the modified barcode and corresponding original properties of the modified barcode stored in the central database are identical, the barcode is considered an original barcode.