I just copy and paste it into google. Although you can use a website called copyscape, but thats unreliable in my experience.
Ive just phoned up a company that have nicked a wedge of text from one of my pages. The guy went off on one telling me what their turnover was (what that had to do with it is beyond me) and that they’re also number one with various search terms in google (what the hell that has that got to do with copyright theft is also beyond me). Anyway, then he moved onto stage two, the ‘lets try and talk over and shout me down’ stage
Anyway, I was eventually told to feck-off and that they’d be blocking my phone number, then he put the phone down, loudly and promptly. Ho humm

Its funny (bizarre funny) when people get angry and can’t maintain an element of dignity because theres a disagreement. I suppose theres other routes by which it can be enforced if talking is out of the equation.