Can I upload past photos?

Yes, and no. 

Situation 1. If you made an observation in real-time at the location it occurred but were unable to capture an image on your smartphone (i.e. you were diving and logged your observations right when you go back on the boat and are now back on land wanting to add photos from your underwater camera to your observations), then yes! Currently this can be done by logging into your account on the web app.

Situation 2. If you have past photos and want to upload them and create observations, then no. This is done because even if the photos are GPS tagged and the user remembers the species, activity and humans on site, the observation lacks context because there is no way to know the full picture. For example, you upload a past photo of a whale you observed but were unaware that a few kilometres away there were loud blasting noises, creating an observation that misses key influences.