I've seen this picture on social media and was wondering why there are 2 Spider-Man (Spider-Men?). What's the storyline of this issue?
This is not from an issue of any of the comics. It's from an episode of the 1967 cartoon.
In the episode Double Identity (S01E19B), an actor turned crook named Charles Cameo is impersonating Spider-Man (and others) while robbing people. Spider-Man, of course, confronts the crook and ends up catching him.