Invincible is an American comic book series by Image Comics. It was created by writer Robert Kirkman and artist Cory Walker and started publication in 2003. Invincible is set in the Image Universe shared by many other Image titles and features a cast of characters similar to that of DC and Marvel comics.
Invincible is not published by either DC or Marvel, but Invincible has had various crossover books with various DC and Marvel characters. For example, Invincible had a crossover with the Avengers, Spider-Man and the Guardians of the Galaxy. Invincible has also had numerous crossovers with other Image titles such as The Walking Dead, Spawn, and Savage Dragon.
So, to answer your question, Invincible is not a DC or Marvel comic, but it does have crossovers with characters from both universes.