Interleaved 2 of 5 (ITF) is a continuous two-width barcode symbology encoding digits.
[4]: §5.3.2 ITF is often used for marking product ID numbers or other codes, of various lengths, on item cartons and multi-unit cases.
One specific instance of this, standardized by GS1, is the ITF-14 bar code used to mark packages with Global Trade Item Numbers.
Since the Bearer Bar is much wider than any legitimate black bar, it will ensure that the short scan cannot appear to begin with the correct start pattern and end with the correct end pattern, forcing an invalid scan.
The barcode is located between the electrically read silver and black DX Camera Auto-Sensing Code and the film can exit lip.