Internal factors that determine the range are related to the characteristics of the thermal system you are using. These parameters are detector sensitivity, lens focal length, lens f-number, thermal detector’s resolution, display resolution and type (small or large), brightness and focus.
External factors involve object size, environmental and weather conditions, the difference between the object and what the background is (complex, open ground, cold clay, hot rocks etc.)
Even your own experience counts.
Look at the images above, happy with that level of ID?
It now becomes obvious that one cannot give a definitive and universal answer to that “how far?” question. Some manufacturers bluntly state detection, recognition and identification figures, or DRI for short without even mentioning what these performance figures depend on; other than a “deer”.
Let’s look at the other end of the scale: You’ve probably seen the nice-looking huge deer, bear or giraffe photos taking up a lot of the image from competitors marketing – ever wondered how far they are? REAL CLOSE is the answer
If they are not showing you images with the distances in New Zealand or Australian locations and conditions then you need to ask why?!
So, the real answer is to have real world local images/videos with ranges so they can see exactly what they will see – it also saves any confusion or false expectations and removes BS from unrealistic figures.