Here's a quick one that I just thought up, so here you go - there is a connective theme going on in these comic covers (could be something about the setting, could be something about the creators, could be a trait some characters on the cover share, could be a lot of things). You have to have some comic book knowledge to get the answer (in other words, it can't be something you can tell just by the cover, like "they all feature blond people!" - you have to have some additional knowledge), and said knowledge isn't as general as "they've all been married" (now if it was "they've all been married and their wife/husband turned into a supervillain," THEN we're talking!). This was a quick one, so I wouldn't be surprised if there was more than one possible theme, but only one that I'm thinking of! :)

Good luck!