Is it illegal to sell products with actors/actresses faces on product?

If I wanted to buy a bunch of iphone cases with the picture of george clooney or brad pitt or even harry potter on them from overseas and sell them on ebay is that considered illegal?

Without their permission the answer is yes.

Well, if the original product was manufactured with the actors' permission via license, it's perfectly fine to resell. If not, you can't resell it at all. It's an intellectual property question of a public figure's right to control their image.

Yes, it 100% is absolutely illegal. Those phone cases for overseas do not have licenses. You are not allowed to make money on selling someone's likeness without their permission.