Visual social media have emerged as an essential brand communication channel for advertisers and brands. The active use of hashtags has enabled advertisers to identify customers interested in their brands and better understand their consumers. However, some users post brand-incongruent content-for example, posts composed of brand-irrelevant images with brand-relevant hashtags. Such visual information mismatch can be problematic because it hinders other consumers' information search processes and advertisers' insight generation from consumer-initiated social media data. This study aims to characterize visually mismatched content in brand-related posts on Instagram and builds a visual information mismatch detection model using computer vision. We propose a machine-learning model based on three cues: image, text, and metadata. Our analysis shows the effectiveness of deep learning and the importance of combining text and image features for mismatch detection. We discuss the advantages of machine-learning methods as a novel research tool for advertising research and conclude with implications of our findings.Instagram is one of the fastest growing photo-and video-sharing social media platforms and has attracted more than 1 billion monthly users worldwide. In the United States, there were approximately 107.2 million Instagram users by 2018, and this number is expected to grow to 120.3 million by 2023 (Nuñez 2020). With its increasing popularity, advertisers and brands have paid attention to Instagram's potential as a brand communication channel in social media. For the term brand communication in social media, we follow the definition of Alhabash, Mundel, and Hussain (2017) and refer to it as brand-related communication distributed via social media that enables Internet users to access, share, engage with, add to, and co-create. This definition includes both brand-generated posts (e.g., advertisements) and user-generated content (UGC) (Voorveld 2019), but we particularly focus on consumer-generated brand communication messages in this study because we are interested in examining how consumers use images and texts when they create brand-related posts in Instagram. Consumers create brand-related posts by using an image of a product with a hashtag indicating the brand (e.g., #apple, #chanel) as a form of brand engagement and loyalty (Phua, Jin, and Kim 2017). For consumers, this combined use of brand-related images and hashtags is a way to find brand-related information and connect with other consumers who have similar tastes (Sung, Kim, and Choi 2018). For advertisers and brands, consumer-generated social media data help to better