I found some similar questions (such as How best to deal with "None of the above" in Image Classification?) but nothing very recent.
In my problem I have 10 trained classes of interest, but occasionally I get a garbage image of some kind, and of course the classifier just guesses from the options it has. Sometimes it spreads the softmax probability out, but often it is fairly confident in one of its choices. This is not unreasonable to me since it lives in a world of "given an image of one of 10 things, which is it?", but it is problematic for a system I intend to integrate into deliverable software.
A "none of the above" class would be okay, but finding training examples for such a thing is a little dicey.
What approaches are effective for this problem?