A lot of people ask and wonder about the legality of emulators and their use. Its much debatable topic, and laws or legalities surrounding with the use of emulators might variate from region to region and even countries.
Emulators are legal to download and use, however, sharing copyrighted ROMs online is illegal. There is no legal precedent for ripping and downloading ROMs for games you own, though an argument could be made for fair use.
An emulator is just a piece of software meant to emulate a game system—but most don’t contain any proprietary code. (There are exceptions, of course, such as the BIOS files that are required by certain emulators to play games.)
More about Playstation Emulators
But emulators aren’t useful without game files—or ROMs—and ROMs are almost always an unauthorized copy of a video game that’s protected by copyright.