Custom Image gain/brightness algorithm for my cameras

Hello, I need a class written in C#. I have several IP cameras and custom software that acquires images from the cameras. Right now, the cameras are set to auto everything (gain, shutter, etc...) I need to manually set all of these settings but as you know, manually setting them will cause problems as things happen such as sunrise/sunset, sun travel during certain parts of the day, shadows, overcast weather, etc... Therefore, I would like to have some code (that needs to be in C# and needs to be fast) that can use the past images to determine if they are a little brighter or darker than usual. I am thinking I can use random images at an interval of x minutes to determine if the camera's images are brighter or darker than usual. In other words, use the camera as a light sensor. Over time, I could then plot and correlate the different readings from this algorithm to what the camera would need to be set at to compensate. I am thinking of something like average lumininance of the picture or a histogram of some sort. Any suggestions and quotes based on your suggestion are appreciated. Thanks!