When it comes to social media, photo posts generally convey positive emotion. Think about your Twitter or Instagram feed. If they look anything like mine do, they're littered with snapshots of sunsets, envy inducing brunch spreads, and gatherings of friends and family.

As reported by the Wall Street Journal, a recent study from Chute, a content-marketing company, confirms this phenomenon. The study -- which analyzed the sentiment of photos and text posts on Instagram and Twitter directed at 30 brands including McDonalds, Delta and Nike -- found posts with images are four times more likely to convey positive emotions than posts with just text, while text tweets are two-and-a-half times more likely to conjure up negative thoughts and emotions than photo posts.

Related: Why Pinterest Is Driving Social Engagement (and How You Can Take Advantage)

The findings make sense. Think about it: It's significantly harder to complain via a photo than it is to do so in a text tweet, which is why Twitter (not Instagram) is the go-to platform for rants about bad customer service. Indeed, a recent study suggests that angry tweets are more contagious than messages expressing sadness, disgust, even joy.

Photos, on the other hand, are a good vehicle for conveying positive sentiment. And that's why, when it comes to advertising, image-based social networks are primed to eat Twitter's lunch. Twitter is good for communicating dissatisfaction, whereas Instagram and Pinterest are aspirational by nature.

Related: Facebook, Twitter or Instagram: Determining the Best Platform for Mobile Marketing

Ads by brands on Instagram garnered 58 times more engagement per follower than Facebook and a whopping 120 times more engagement per follower than Twitter, according to a recent study by the market research firm Forrester.   

This could be because while promoted tweets stand out (immediately obvious, at least to me, as advertising) promoted posts on Pinterest and Instagram are far less blatant. Users are already organically posting photos of aspirational products, so ads for luxury retail, beauty and fashion lines don't feel out of place and generate high levels of engagement. A pinned photo on Pinterest of a pair of pants sponsored by Banana Republic often receives just as many clicks as an image of a pair of pants organically posted by a friend, Pinterest spokeswoman Malorie Luchich told  New York Magazine. "Users don’t really look at them as ads."

If you're a brand with a photogenic product to sell, consider advertising with a photo on Instagram or Pinterest. Save Twitter for responding to customers who have already bought your product and – for whatever reason – want to complain about it.

Related: Instagram's 5 Tips for Better Marketing -- With Pictures

Related Book: Ultimate Guide to Pinterest for Business