Some barcode symbologies feature optional checksum/check-digit while for others this is mandatory.

For example, Code 128, GS1-128, EAN/UPC barcodes have a mandatory checksum/check-digit value which is used to ensure the reliability of the barcode symbol. For these kinds of symbologies, the Barcode Reader SDK takes advantage of the checksum and will only decode those barcodes which checksum is valid. If the checksum/check-digit is not valid, then the Barcode Reader will not decode the symbol.

On the other hand, there are some symbologies with optional checksum/check-digit like Code 39 and Interleaved 2 of 5. For example, some Code 39 barcodes are generated using a Mod43 checksum. If you know that the barcodes (of optional checksum symbologies) on the source image have a checksum/check-digit incorporated, then you should enable this on the BarcodeReaderHints object attached to the BarcodeReader object. For example, for Code 39 Mod43 checksum, you should enable (set it to True) the Code39EnableMod43Checksum property. Look at the properties of the BarcodeReaderHints object for additional checksums for other symbologies like Interleaved 2 of 5.