Imperial Cult
Pompey
After Pompey was killed, and Augustus came to power, Augustus found it useful to allow this emperor-worship to continue (and I don't know that he could have stopped it anyway). So people in West Asia and Egypt continued to worship the Roman emperors as gods right up until everybody converted to Christianity in the 300's AD. In fact, emperor worship was one of the last parts of the pagan tradition to stop, well into the 400's AD.
You might say that it was ridiculous to worship a person as a god, but it wasn't as ridiculous as it seems to you. The Romans worshipped a lot of gods, some more powerful than others, but none of them as powerful as the God that Christians, Jews, or Moslems think of today. And there were many less powerful gods too. Why shouldn't the emperor be one of them? The emperor was just as remote to most people as the gods, you never saw him, you never spoke to him (or he never spoke to you anyway). And he was just as powerful: he could send food when there was a famine, he could make there be a canal where you needed one, he could have a whole city full of people killed if he liked. In fact, he probably did all of these things more often than the gods did. So why not pray to him?
A useful book on Roman religion is Ramsey MacMullen's Paganism in the Roman Empire. His writing is very lively, and he uses a lot of interesting stories from the Roman world to illustrate his points. No pictures though.