Mediawiki Error: “Error creating thumbnail: Unable to save thumbnail to destination”

I have an older Mediawiki installation which, after upgrading to version 1.23.0, I began to see errors like:

Error creating thumbnail: Unable to save thumbnail to destination

The problem turned out to be the temporary folder setting in LocalSettings.php. It was pointing to ‘tmp’ under ‘images’, which didn’t exist. Instead, there was a folder named ‘temp’. The solution was to change:

$wgTmpDirectory     = "{$wgUploadDirectory}/tmp";

into:

$wgTmpDirectory     = "{$wgUploadDirectory}/temp";