how do you know if a dvd is fake?

sometimes I get my hands on some dvd movies that are very low quality....i think some of them are dvds made out of TCs or avi...is there a way to find out if this are real dvds?

thanks

 

look at the disc used, also writing round center, colour of the back dye, if got menus, and picture quailty.

not sure what your after?

but basically buy from a shop, pay alot of money and the disc comes pretty boxed sealed!