The identification of credit card encoders by hierarchical cluster analysis of the jitters of magnetic stripes

The relative bit density variation graphs of 207 specimen credit cards proc essed by 12 encoding machines were examined first visually, and then classi fied by means of hierarchical cluster analysis. Twenty-nine credit cards be ing treated as 'questioned' samples were tested by way of cluster analysis against 'controls' derived from known encoders. It was found that hierarchi cal cluster analysis provided a high accuracy of identification with all 29 'questioned' samples classified correctly. On the other hand, although vis ual comparison of jitter graphs was less discriminating, it was nevertheles s capable of giving a reasonably accurate result.