Are ROMs legal

The legality of ROMs has never been directly tested in court. In Atari vs. JS&A, it was decided that backup cartridges (basically a cartridge with the ROM on it so you could play it on the Atari) were not legal under United States copyright law. The ESA, an organization with members consisting of several game publishers, routinely prosecute the illegal selling and trading of protected games, be they in physical or digital format.

ROMs that are written by a hobbyist and released on the internet for everyone to download are irrevocably legal.