I see a two-pronged answer.
1) What is the photographer/creator's intent?
2) What is the viewer/public's perception?
A photograph of a factory on fire would be considered journalism if the photographer's intent was to document the incident but if he made the photo with a different mindset, the very same photo would be considered art. On the other hand, if the photo was printed beneath a headline in a newspaper, Acme corporation on fire!" the public would perceive it differently than if it was framed and hung in a gallery.
Does the medium in which the photo is presented affect how viewers perceive it?
To a degree, I think it does but I think the medium is only the intermediary which conveys intent.
On the other hand, the very same Polaroid or Instax photograph would be perceived as having a different intent depending on whether it was presented in a pile on a coffee table, whether it was mounted in a scrapbook or whether it was framed and hung on the wall.
So, yes, I think a Polaroid CAN BE considered art if the photographer presents it in a way that conveys artistic intent to the viewer.