Currently, there is no standard quantitative measure of the performance of an image-based tracker algorithm. It is usually described as remaining in track for the entire run or losing track at some point during a run. This is purely a qualitative evaluation. Without a quantitative measure it becomes difficult to accurately evaluate the performance of a tracker algorithm. We have developed the Tracker Performance Metric (TPM) specifically for this purpose. It was designed to measure the output performance, on a frame-by-frame basis, using its output position and quality (sometimes referred to as confidence) state. The TPM can also be used as a measure of algorithm performance to compare against the Trackability Metric. The Trackability Metric was developed by AMCOM to determine how trackable a set of data should be. The TPM will be described and results presented.