Many of the Cognitive Services have a free tier you can use to try the service. To use the free tier, use F0 as the SKU for your resource.
There are two tiers of keys for the Custom Vision service. You can sign up for a F0 (free) or S0 (standard) subscription through the Azure portal.
Incorrect Answers:
A: There is no free tier (F0) for ComputerVision.
Reference:
https://docs.microsoft.com/en-us/azure/cognitive-services/cognitive-services-apis-create-account-client-library?pivots=programming-language-csharp
https://docs.microsoft.com/en-us/azure/cognitive-services/custom-vision-service/limits-and-quotas
