Creating predefined questions with known answers is honey pots [54]. If the workers answer these questions correctly, they are marked as appropriate for this task
Some qualification settings are set when creating HITs
AMT, Crowdflower
Using approval rate
Trap questions
This method is about designing HITs along with a set of questions with known answers to find unreliable workers [58]
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CAPTCHAs and reCAPTCHA
CAPTCHAs are an antispamming technique to separate computers and humans to filter automatic answers. A text of the scanned page is used to identify whether human inputs data or spam is trying to trick the web application as only a human can go through the test [59]. reCAPTCHA is the development of CAPTCHAs [60]