What distinguishes photography from other visual mediums? This deceptively simple but fundamental question has been at the centre of both past and current debates on the aesthetics of photography for quite some time. In this article, I will first address the premise that this question is intrinsically ontological and unfolded in pioneering debates as a sequence of implications about photographic indexicality. I will then argue that the ontological implications of photographic indexicality have been largely overlooked in subsequent research due to scholars' concerns with how photography appears to us rather than what photography is in itself. To this end, I will specifically examine Kendall Walton's highly contested transparency thesis and some of its rebuttals, which have exerted a sprawling influence on debates on the aesthetics of photography. I will also argue that, having been exceedingly implicit in his account, what appears as indexicality to Walton and the implications thereof with respect to the transparency argument has operated on a phenomenological level; thus, the thesis itself has failed in instances in which the problem of representation and the very existence of the medium come into play. Finally, I will suggest that indexicality can be regarded as a distinctive feature of photography only when it is considered a predicate of transparency as an interstice of 'unconcealment' in the Heideggerian sense that would call into question the very existence of the representation and the photographic medium.