Online social media has been a popular source for people to consume and share news content. More recently, the spread of misinformation online has caused widespread concerns. In this work, we focus on a critical task of detecting fauxtography on social media where the image and associated text together convey misleading information. Many efforts have been made to mitigate misinformation online, but we found that the fauxtography problem has not been fully addressed by existing work. Solutions focusing on detecting fake images or misinformed texts alone on social media often fail to identify the misinformation delivered together by the image and the associated text of a fauxtography post. In this paper, we develop FauxWard, a novel graph convolutional neural network framework that explicitly explores the complex information extracted from a user comment network of a social media post to effectively identify fauxtography. FauxWard is content-free in the sense that it does not analyze the visual or textual contents of the post itself, which makes it robust against sophisticated fauxtography uploaders who intentionally craft image-centric posts by editing either the text or image content. We evaluate FauxWard on two real-world datasets collected from mainstream social media platforms (i.e., Reddit and Twitter). The results show that FauxWard is both effective and efficient in identifying fauxtography posts on social media.