[header] How to use footprints in detecting [title] Observe the footprints. [step] Get yourself a good magnifying glass for the finer details, or at least good eyesight for spotting the footprints. [title] Measure the footprints. 
[step] The size of a person's shoe usually gives the height of the person to a given range. This ratio is rather accurate; however there is a certain percentage of the population, around 10-20%, which this deduction would not apply.