No way to report errors on image questions
This morning Duo showed me a picture of a camera and asked me to give the German word for "the camera". I entered "der Fotoapparat". So far as I know, that is correct, but Duo says it's wrong. Duo is looking for "die Kamera". That's fine. But on this form of question (you're presented with a picture and expected to provide the word), there is no way to report "My answer should be accepted" like there is on most other forms of questions. On this form of question, the one and only option you're give is to report that the image doesn't match the given word.
If this camera deal was the one and only time I've encountered this situation, I'd be tempted to ignore it. But this actually happens fairly regularly, and it's frustrating that there is no way to report the problem.
I agree; it would be useful to be able to submit feedback directly.
The next best thing is to post in the forum a bit like you did, while mentioning the picture, the English word, and the German word(s), as well as in which lesson of which skill you had this problem.
There are dozens of skills in the tree, and it's a lot fast to find the problem if we know exactly where to look... and less work for us makes it more likely that we'll get around to it in a timely manner :)
Unfortunately, we can't monitor all the forum discussions all the time, so we may miss such a forum report.
But we may also miss "proper" reports -- there are thousands and THOUSANDS of reports in the backlog and it's impossible to give them all the attention they need. Sorry.
You should keep track of which users give useful feedback and give them some kind of priority in your efforts to fix errors. (Then again, maybe you already do something like that.)
In the future, I'll do like you suggest and report issues like my image problem in the discussion forum for the question. I've hesitated to do that in the past, because I thought that was frowned upon. At the moment at least, I guess there is no better way.
I know in a much earlier version of Duolingo, back before ads, when human powered web content translation was still the vision, there used to be a text input box on the error reporting dialog (I think in addition to the multiple choice options we have today). That was nice, because it gave the person reporting the problem the opportunity to explain their reasoning, or call out unanticipated problems like my issue with the image question. I've always wondered why the developers chose to remove that feature. Surely the more detail you can get in the feedback, the better off you are, right? I wish they would bring that back.
I was both sorry and interested to hear there is such a big backlog of error reports. I have wondered how things work behind the scenes. Who looks at those reports anyway, and how is the final decision made to accept or reject a suggested change?