Contact
One person reads this. Expect a reply within a couple of days.
A capture came back wrong
Check the articles first — cut-off captures, repeating headers, blank images and one-screen results each have a page explaining the cause. If none of them match, email the URL of the page and a description of what you got instead.
Bug reports
The most useful report includes the page URL, your Chrome version, your operating system, and what you expected versus what happened. A screenshot of the wrong screenshot is genuinely helpful.
Privacy and security
Questions about data handling are answered in the privacy policy. If you have found a security issue, email it rather than filing it publicly and allow reasonable time to fix it before disclosure.