Assuming two observations with identical photo, having two organisms one at left and one at right, neither being clearly more significant than the other, and assuming there is no description or indication from the observer (such as an ID of one of them) to indicate which is the subject of the observations:
Encountering the first observation and being the first to ID, I would ID as the one on the left. I would then leave a comment that “I am assuming the subject to be the one on the left, please let me know if this is not so”
Encountering the second, and again being the first to ID and assuming I remember having seen the other observation, I would go back to that other observation to compare to this one, and seeing that they are the same photo but two possibilities for subject, I would ID as the one on the right, leaving a similar message as to the first.
If, on the otherhand, one of the organisms is slightly more “significant” in the photo, then as above, but substitute “most significant” for left, and “second most significant” for right.