I would bet the issue is the temperature sending unit (the part on the car which reports the actual temp to the computer/gauge). These sensors work off of resistance. As the temperature gets higher, more resistance is introduced and less voltage gets through. The voltage is read by the computer and then knows the temperature based on a predetermined scale. In your case, the resistace is steady no matter what the temperature and therefor the gauge is reading steady without deference to the actual temperature of the engine.
I'm not sure how the Camry is setup, as in whether it uses one sensor for both the computer and the gauge, or two sensors with one for each. If the car uses one for both, this will also affect how the car runs as the PCM uses the temperature of the engine to determine how much fuel is needed for optimal running.
I would give you more advice on fixing the issue and how to test things, but you didn't provide enough data about the car itself.