Increased interest in the use of the scanning infrared camera as both a diagnostic and research tool by the medical profession has led to the need for an external temperature reference. The scanning infrared camera detects the infrared radiation leaving a surface and converts the energy into a visual image which is photographed and termed a thermogram. This paper presents a thermal reference made by constructing an extended surface or fin in such a way as to produce a linear temperature profile down the fin axis. A fin was made following the theoretical model and tested. The resulting fin was quite linear and provides an excellent thermal reference.