I used the Fatkun image downloader. It has been mentioned in the forums in another topic. My dataset consisted of 670 images.
Thanks for showing me the importance if having an ‘I don’t know’ class. I feel there are two ways of making the Neural Network say “I don’t know” :
Create a new class labeled as ‘unknown’ and fill it up with images of everything that is not related to your problem. However, this is very unrealistic.
Try to extract the features from the Neural network and pass the features through a Machine Learning classifier (Like a decision tree or SVM). This method however requires us to get some knowledge on Neural Network theory.