Neural networks are widely used to solve image recognition problems: detecting pedestrians and vehicles for self-driving car, identifying people for security systems, identifying gestures for a videogame controller.
I wanted to learn how to use neural networks for image recognition, so I should have a quite large dataset of labeled images to train a neural network. Preparing such a dataset is not an easy job. Hopefully there are open source datasets for different purposes. Most frequently used dataset for image recognition is MNIST (Mixed National Institute of Standards and Technology database). It is a large database of labeled hand-written digits like these: