We have requested that annotations can be added during upload - https://forum.inaturalist.org/t/lets-talk-annotations/627/6
One can add annotations during upload by using fields - https://forum.inaturalist.org/t/lets-talk-annotations/627/267 - but you have to know this, and you have to know exactly which fields.
The fields-to-annotations method also causes problems and I have observations fail to index - https://forum.inaturalist.org/t/not-all-observations-uploading/4946/86 - and I also find the annotations take ages to ‘take’ - https://forum.inaturalist.org/t/a-faster-annotation-modal/9571/9
BUT, I’ve had an idea (!) If we had leaderboards for annotaters, I’m pretty sure this would increase annotation volume. The leaderboards for identifiers cause ‘problems’ when people agree to IDs just to go up the board (not because they necessarily have any clue about the correctness of the identifications), and this particular leaderboard has now been removed from the Identify page. Why not let’s use this to our advantage, and get 'em annotating 