help with resnet50 and identifying previously unencountered objects

I need help in coming up with a technique to determine when an object is not in the list of already classified objects.

I am sorting parts that are the identical shape, but differ in the text written on them. Unfortunately the text is written in a circle, so I can’t simply read the text with OCR. (At least I couldn’t make it work.)

I have about 20 different labels on the parts I currently have. Some parts I have 1,000 pictures of, others I only have 100 pictures.

I discovered while I was sorting that there are actually more than 20 different labels, there are parts I didn’t know about that only occur once or twice in five hundred parts. I would like to be able to identify and handle parts like this separately.

I am using keras.resnet50 to classify the images (parts). I get about a 96% accuracy of a part being identified correctly when I use two different classifiers to look at the same image and then check their agreement. I do this because I would rather reject parts than have them sorted incorrectly. Classifier two just has a different number of epochs than classifier one.

My images are 300×300.

I look at the weight of the prediction, and 95% of my predictions are almost certain, say .99999, so I haven’t been able to do the simple thing of just looking at the strength of the prediction.

In case this is relevant, the resnet50 classifier that I have trained might be overtrained. Within three epochs it is at like 99.7% accuracy with a val_accuracy of 98%.

Epoch 3/3

99/99 [==============================] – 572s 6s/step – loss: 0.0138 – accuracy: 0.9967 – val_loss: 0.3574 – val_accuracy: 0.9796

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Any ideas?