What do you call a painting or picture with many different things on it?

Well see, my friend has a desktop background with like a hundred different things on it. you always spot something different everytime. like a tiny man fishing on a boat, or a panda with its paw on a train. it was so imaginative and it was all like one little world.. i was thinking of getting one, but i'm dont even know the word to google! please help~~ thanks