This paper presents the results of a study which explored the use of Flickr by cultural heritage institutions. The study examined two aspects of museums' use of Flickr: the content of images posted by museums, and the reasons behind sharing their images to the social media site. Images were categorized by the researchers into nine classes based on their visible content, and a brief questionnaire was used to gather data about the image sharing process from museum personnel. The findings reveal that imagery of people visiting the museum and taking part in museum events predominated in the total number of images posted by museums (54% of the total). The images posted to Flickr were most often selected by a single individual at the institution. The particular images posted to Flickr were chosen for a variety of reasons, the most common of these being that they were newsworthy recent events at the museum (e.g. openings, exhibitions, lectures, etc.), or that the staff found the images to have strong affective characteristics. In the responses from museum staff regarding the motivations behind posting the images to Flickr two replies were most commonly given: to provide access to the images, and to take advantage of the technical benefits provided by the photo-sharing service.