Fueling the Gold Rush: The Greatest Public Datasets for AI by Luke de Oliveira via @StartupGrind

Though not at the forefront of the AI hype train, the unsung hero of the AI revolution is data — lots and lots of labelled and annotated data—curated with the elbow grease of great research groups and companies who recognise that the democratisation of data is a necessary step towards accelerating AI....Most people in AI forget that the hardest part of building a new AI solution or product is not the AI or algorithms — it’s the data collection and labelling. Standard datasets can be used as validation or a good starting point for building a more tailored solution.

There is a wealth of data out there and it is a good starting point as long as you are careful and don't rely on data that you cannot guarantee is correct and accurate.