1. A method for estimating a heart period using at least one of a plurality of electrocardiogram recordings, comprising: utilizing a computer processor to convert a plurality of the electrocardiogram recordings into a plurality of corresponding electronic electrocardiogram images; deriving an electrocardiogram waveform from one of the electronic electrocardiogram images by extracting an upper envelope and a lower envelope of the electrocardiogram waveform from the corresponding electronic electrocardiogram image using a curve tracing algorithm; determining an electrocardiogram signal peak from increased thickness at the electrocardiogram signal peak due to pixel dithering; determining a difference between the upper envelope and the lower envelope at the electrocardiogram signal peak and at an electrocardiogram low point, which are a local maximum and a local minimum of one of the corresponding electronic electrocardiogram images; and estimating the heart period.