Research on journalists' social media practices has not yet developed clear platform specificity; that is, how these practices might differ according to a platform's unique culture and vernacular affordances. This paper explores how journalists have mediated aspects of Instagram's unique visual cultures within their professional journalism practices. It argues journalists develop representations of their professional identity and role using mediated journalistic practices that also adhere to Instagram's culture and "vernacular" social practices. Using a visual content analysis and semi-structured interviews with Australian journalists, this paper shows that journalistic practices on Instagram are context-specific and dynamic. Unique journalistic practices develop and change according to the journalist's perception of professional need for, and personal satisfaction with, Instagram's specific culture of interaction, its vernacular communication practices, and professional and personal communication outcomes. This is important to establish how journalistic practices are negotiated within Instagram's visual cultures, and the consequences for changing practices on production, distribution, and audience reception of news on the site.