Manual:$wgThumbnailEpoch

From MediaWiki.org

Cache: $wgThumbnailEpoch
If rendered thumbnail files are older than this timestamp, they will be rerendered on demand as if the file didn't already exist.
Introduced in version:	1.6.0 (r11945)
Removed in version:	still in use
Allowed values:	timestamp (string)
Default value:	'20030516000000'

Other settings: Alphabetical | By Function

[edit] Details

If rendered thumbnail files are older than this timestamp, they will be rerendered on demand as if the file didn't already exist. Update if there is some need to force thumbs and SVG rasterizations to rerender, such as fixes to rendering bugs.

See also: Manual:$wgCacheEpoch