Alternatively, watch the LED (Score 1)

The meter should have an LED that pulses at a rate equal to the rate of consumption (the pulses/kWh will be written on the meter near the LED). It's an easier programming exercise to measure this, but you have to continuously monitor it and can't just take snapshots.

If the meter is really old it might have a rotating disk with a mark on it. You still get a pulse, but the image-processing exercise isn't much simpler than reading the numbers.