i'm no expert, but i believe machine learning / classification algorithms can help you on this. you just need to train the algorithms on what you want to find.

'finding' objects means feeding the algorithms a series of 'features' that you extract from video and normalize into data structures - color, corners, edges, velocities, relative distances, etc, which are then fed into the algorithms to produce a classification or a probability.

analyze every Nth frame and try to classify found objects. if a known object is found, do something.