Given their inherently corny appearance, stock images are more often the fodder for online jokes than anything else. The "I bet he's thinking about other girls" meme stands as one such example. For the uninitiated, this meme is a photo of an unamused girlfriend looking in an annoyed fashion at her boyfriend, who appears lost in thought.
According to the jokesters of the internet, other girls are the last thing on this BF's mind, who would rather concern himself with philosophy, childhood cartoons, and the capitalist food chain. Much like the infamous "Is this a pigeon?" meme, the "He's probably thinking about other girls" meme offers a ton of versatility.