Error creating thumbnail: convert: Unrecognized option (-thumbnail).
Fragment of a discussion from Project:Support desk
You don't have image magick installed, or more likely have another program thats not image magick installed with the name convert.
You need to either set manual:$wgUseImageMagick to false in LocalSettings.php, or install image magick, or fix where mediawiki is looking for image magick (manual:$wgImageMagickConvertCommand).
