that’s a pleasant surprise.
taking that synthetic picture from the old site as an example, you’d wanna prepare the picture so the red markings are ignored. you only care about the black marks.
take scanlines along the length, at various positions into the width of the tape. 1D signals are easier to analyze. run one over the mm ticks, one that only intersects cm ticks.
the black ticks are local minima in the signal. there are many ways to find local extrema. you’ll need to fiddle with smoothing and thresholds and such, but only once.
going from the cm ticks, you could blindly grab a ROI that must contain a number. send it to whatever OCR you want. this could be very cheap to OCR, if you’re willing to specialize the OCR. it’s just digits of a single appearance (font, size, …)