Screenshots of issues is something we support in many of our paid offerings, but not in axe-core itself. It sounds like the Slack folks implemented their own version of it.

If you have general questions about axe-core, the best place to ask is our axe Community slack instance (https://accessibility.deque.com/axe-community). If you have a specific issue you'd like us to investigate, try https://github.com/dequelabs/axe-core/issues