What services do ML/AI researchers use to get training data? (Amazon's Mechanical Turk, CrowdFlower)
What kinds of tasks do researchers post to those services? Are tasks usually a variant of classification tasks*?
I am trying to collect some data from ML researchers, practitioners or hobbyists.
* User can select one of the classes (options) provided as solution to the task.
E.g. Is this product a  Electronics Product  Beauty Product  Health Product?