I agree, it’s going off topic. This topic is a feature request, not a question - and the motivation for the request is that sometimes the same photo is uploaded multiple times for the same organism. The feature is not intended to prevent people from using the same image for multiple organisms, just to ask them if they need to upload the photo again.
While I agree it’s better to upload one photo to use for observations of multiple organism within the photo, having the same photo uploaded twice for two different organisms isn’t a serious problem. What this comes down to, I think, is will the benefits of some sort of messaging asking users if they want to upload a photo again be worth the confusion it may cause?