I do not usually chime it, but.
Owning a ROM to a game means that ROM is for that game. Porting the ROM over to a different platform is not legal.
As in, if you own Galaga on a real game machine and use the ROM you copied over on an emulator, it is illegal.
If you own a floppy disk of a game for C=64 and used on an emulator its illegal.
But, some companies now think that it is ok to PD some roms.
If someone makes a profit of selling ROMs thats a No No..
On the other hand, like I said, some ROMs are or could be PD because companies no longer hold rights.
Will a company go after someone selling a flash card of 25,000 images.. Don't know. Will they make a $$ going after someone, Maybe, maybe not.
Unless time has changed and I missed something along the way, copyrights are still in effect for some.
They probably go after someone who sells movies faster than a ROM of an old system.