How to label "other" while labeling image for object detection/classification?
This highly depends on your test data. Suppose you have trained your data which all contains some kind of food. If you give it a hand at test time, it will try to find the most similarity it has with the current labels and outputs the one which is more similar than the others. The point is that your test environment is really important. If you are going to test your app near the sea, your training data set should contain data on that condition. If you are going to use it during the night, your dataset should be taken during the night. In your case, you have a simple task, for the current dataset add an entry with a zero which means you are trying to add a new class. After that, try to add new pictures that are not images of food and add one in the new entry for these images. But consider this important point. The number of images in each class should have the same distribution as the test data.