Did you know that tweets that include images are more likely to be retweeted than tweets without images? Research has shown the increase to be anywhere from 34% to a whopping 94%! Obviously you don't need to add a picture with every single tweet, but keep in mind that your tweets with pictures will be slightly more engaging to your followers.
With the addition of expanded images on Twitter last November, images are an even bigger part of your Twitter feed. When tweeting through the Twitter website or the Twitter app, adding a photo will result in a preview image showing up directly in your feed, rather than just a link. The expanded images not only draw the eye to your tweets, they also directly lead to more clicks, more favorites, and more retweets.