MediaModeration

This section describes the configuration and operation of maintenance scripts associated with mw:Extension:MediaModeration and the MediaModeration 2.0 milestone.

Processing images manually, January 2024

As of January 2024, we are running extensions/MediaModeration/maintenance/scanFilesInScanTable.php manually on Wikimedia Commons. The invocation on mwmaint2002 is:

Manual processing

# Using `tmux`
mwscript extensions/MediaModeration/maintenance/scanFilesInScanTable.php --wiki=commonswiki --use-jobqueue --sleep 30 --last-checked 20240312 --verbose 2>&1 | tee ~/scan-files-in-scan-table-commonswiki-sleep-30-no-render-now.txt

Once we have completed processing the Wikimedia Commons backlog, we will shift to a new phase of the project, where we update operations/puppet repo to process images on a daily basis.

Overview

Add items to scan table on upload
Obtaining thumbnail for files and sending file contents to PhotoDNA
Distribute scanning work by image (SHA-1) using the job queue
Use sleep to manage rate limits and target 10M requests per month
Update last_checked value always. Update mms_is_match if PhotoDNA gives us a response
Database
- Uses an external store
- Has three columns:
  - mms_sha1 - can be a match with a SHA-1 in filearchive, image, or oldimage tables
  - mms_last_checked not a MW timestamp, instead uses a shorter format e.g. 20240130 to track day but not time
  - mms_is_match - 1 if the SHA-1 matches, 0 if the SHA-1 was not a match, NULL if no successful scan has occurred yet.

For each SHA-1 value to be scanned, do these steps:
- Iterate over all rows in filearchive, image, and oldimage tables that have the given SHA-1:
  - Check if the image for this row can be scanned by PhotoDNA, otherwise continue to the next row.
  - Attempt to get a suitable thumbnail for the image, and if successful then attempt to get the contents of the thumbnail
  - If the thumbnail or thumbnail contents cannot be generated, then try to get the image contents. If the image contents is not suitable then continue to the next row.
  - Send the image contents to PhotoDNA. If the request fails, then continue to the next row. If this is successful, then end the loop early.
- Save the new match status returned by PhotoDNA (NULL is the match status if no row was successfully used to scan the SHA-1).
- If the new match status is positive, send an email indicating a match.

Metrics

Once a day, we emit the following metrics (MediaModerationMetricsFactory):

the total table count of the mediamoderation_scan table for a given wiki
the number of scanned images (mms_is_match IS NOT NULL) in the mediamoderation_scan table
the number of unscanned images (mms_is_match IS NULL) in the mediamoderation_scan table
how many unscanned images (mms_is_match IS NULL) which also have been previously attempted to be scanned (mms_last_checked IS NOT NULL) are present for a wiki

The updateMetrics.php script emits these metrics for all wikis via the mediamoderation.pp puppet module (patch).

The metrics are visible on the MediaModeration PhotoDNA dashboard.

PhotoDNA

Credentials are available in the Trust and Safety Product team's 1Password
Rate limits as of January 2024:
- 200 requests per second
- 10 million requests per month