An imager captures images of a living subject including a near-infrared image, an infrared image, or both. A processor is connected to the imager and an output device. The processor is configured to generate output images of vasculature of the living subject from the images captured by the imager, include in the output images a range of discrete scale comparator objects of different sizes, and provide the output images to the output device for display to a user. The range of discrete scale comparator objects may have sizes that are representative of the different sizes of peripheral IV catheters available. They are visible as juxtaposed with imagery of the vasculature, so that the user may make a direct visual comparison in order to ascertain a suitable size of peripheral IV catheter.
