1. A method of analyzing changing events comprising: scanning a first image field during a first interval of time with a sensing means and generating a first video signal on the output of said first sensing means, computer processing and analyzing said first video signal and generating first code signals indicative of characteristics of the image content of at least a portion of said image field scanned, recording said first code signals in a first memory, scanning said first image field a second time with said sensing means and during an interval which occurs after the completion of said first scanning operation and after a change has taken place in the contents of the image field scanned, and generating a second video signal on an output of said sensing means, computer processing and analyzing said second video signal and generating a second code signal, recording said second code signal in a second memory, reproducing said first and second recordings of said first and second code signals from said first and second memories, computer analyzing said first and second code signals and automatically detecting differences therein, and generating a third code signal defining information about said change in said image field, recording said third code signal, thereafter repeatedly scanning said image field a number of times and repeating the procedure of computer analyzing each video signal generated, and generating further code signals defining further changes in the content of the image field occurring between each of said scannings, recording said latter code signals as they are generated and further computer analyzing same in a manner to detect changes in the content of the image field over an extended period of time and determining a trend in the change in image content of said image field.