Add a 'Report' button to the video or image page, with a drop down list of different reasons to report.
-incorrect SFW/ecchi setting
An option to report spam/forbidden comments might be desirable as well.
Users are more likely to report bad content.
Duplicate reports can be automatically consolidated, easing mod workload.
Problem/malicious reporters can be flagged and banned from reporting.
Requiring the reporter to be logged in and provide a short text message describing the problem would discourage report spamming.