For resizing images DokuWiki uses PHP's libGD if available. DokuWiki tries to detect the availability and version of libGD automatically. However, in older PHP versions, this does not work. You can force a version by setting this variable. Possible values are: '0' for no libGD support; '1' for libGD version 1.x; and '2' for libGD 2 with autodetect.