Whether they come in the form of ideas you can't get out of your head or nightmares that appear repeatedly in your sleep, recurring images are something we all experience.
I've been working a lot with recurring images in my writing lately. I started paying attention to this technique after reading Proust's In Search of Lost Time and then moving on to Ishiguro's Never Let Me Go and Remains of the Day. Both of these writers deal a lot with the idea of unreliable memory. The narrators of these stories recall memories, but they admit that the memories might be inaccurate. Under these circumstances, recurring images are important because they suggest that whatever is recurring is somehow meaningful to the narrator, even if she or he doesn't understand them. A recurring image weighs more heavily in the narrative, even if it's not presented in any emphasized way.
Maybe this is a simple concept, but I think there's a really wonderful nuance to the recurring image relative to a character's experience. That nuance has to do with the idea of passivity.
When we have recurring nightmares or recurring ideas, we are rarely in control of them. They bob up in our minds when we least expect them. They call attention to themselves. "Pay attention to me! Hey, check me out, I'm totally recurring!"
A writer can create an eerily realistic situation by having their character experience recurring images. In a sense, you are creating an unconscious mind for your character...and if that isn't a remedy for a flat character, I don't know what is.
I love the effect a recurring image has on a character. It makes me feel like the character's mind is working constantly. It creates a parallel inner working to the external events. In my current story, Cyberlama, my narrator had a lot of experiences early in her life that she didn't fully understand. As these memories come back to her, she can reflect on them, grow from them, and I think it really enhances the character development I'm trying to create.
Have you played around with recurring images? How did they work for you? What purpose did they serve?