Decode delegate missing for Image Gallery Plugin

This example is provided in VARIMAGEGALLERY:

%IMAGEGALLERY{"System.DocumentGraphics" columns="3" limit="12" exclude="arrow" sort="name"}%

But when I try to use this with a new installation of V1.1.2, I receive the following error:

Error: Exception 420: no decode delegate for this image format `/var/www/vhosts/copswiki.org/httpdocs/w/pub/System/DocumentGraphics/addon.png'

Also, I have a number of regular errors in error.log

| 2011-02-08T04:09:55Z warning | Foswiki::Plugins::ImageGalleryPlugin::Core | attachment error in System.DocumentGraphics: no such file '/var/www/vhosts/copswiki.org/httpdocs/w/pub/System/DocumentGraphics/blank-bg.png' | 
| 2011-02-08T04:09:55Z warning | Foswiki::Plugins::ImageGalleryPlugin::Core | attachment error in System.DocumentGraphics: no such file '/var/www/vhosts/copswiki.org/httpdocs/w/pub/System/DocumentGraphics/blank.png' | 
| 2011-02-08T04:09:55Z warning | Foswiki::Plugins::ImageGalleryPlugin::Core | attachment error in System.DocumentGraphics: no such file '/var/www/vhosts/copswiki.org/httpdocs/w/pub/System/DocumentGraphics/empty.png' | 
| 2011-02-08T04:09:55Z warning | Foswiki::Plugins::ImageGalleryPlugin::Core | attachment error in System.DocumentGraphics: no such file '/var/www/vhosts/copswiki.org/httpdocs/w/pub/System/DocumentGraphics/monospace.png' | 
| 2011-02-08T04:09:55Z warning | Foswiki::Plugins::ImageGalleryPlugin::Core | attachment error in System.DocumentGraphics: no such file '/var/www/vhosts/copswiki.org/httpdocs/w/pub/System/DocumentGraphics/proportional.png' |

-- RaymondLutz - 08 Feb 2011