We present and analyze a database of 1.13 million public Instagram posts during the Black Lives Matter protests of 2020, which erupted in response to George Floyd's public murder by police on May 25. Our aim is to understand the growing role of visual media, focusing on a) the emergent opinion leaders and b) the subsequent press concerns regarding frames of legitimacy. We perform a comprehensive view of the spatial (where) and temporal (when) dynamics, the visual and textual content (what), and the user communities (who) that drove the social movement on Instagram. Results reveal the emergence of non-institutional opinion leaders such as meme groups, independent journalists, and fashion magazines, which contrasts with the institutionally reinforcing nature of Twitter. Visual analysis of 1.69 million photos show symbols of injustice are the most viral coverage, and moreover, actual protest coverage is framed positively, in contrast with combatant frames traditionally found from legacy media. Together, these factors helped facilitate the online movement through three phases, culminating with online international solidarity in #BlackOutTuesday. Through this case study, we demonstrate the precarious nature of protest journalism, and how content creators, journalists, and everyday users co-evolved with social media to shape one of America's largest-ever human rights movements.