Having previously had troubles with ImageMakic which were solved with help from here and discussions with my hosting provider, I now get this error when adding a file:
----------------------------------------
Omeka has encountered an error
Omeka_File_Derivative_Exception
ImageMagick failed with status code 127. Error output:
sh: -background: command not found
#0 /home/xxxxxx/public_html/om/application/libraries/Omeka/File/Derivative/Image/Creator.php(107): Omeka_File_Derivative_Image_Creator->_createImage('/tmp/4ed5070306...', '/tmp/fullsize_4...', '-background whi...')
#1 /home/xxxxxx/public_html/om/application/models/File.php(362): Omeka_File_Derivative_Image_Creator->create('/tmp/4ed5070306...', '4ed5070306ab90e...', 'application/pdf')
#2 /home/xxxxxx/public_html/om/application/models/Job/FileProcessUpload.php(22): File->createDerivatives()
#3 /home/xxxxxx/public_html/om/application/libraries/Omeka/Job/Dispatcher/Adapter/Synchronous.php(25): Job_FileProcessUpload->perform()
#4 /home/xxxxxx/public_html/om/application/libraries/Omeka/Job/Dispatcher/Default.php(136): Omeka_Job_Dispatcher_Adapter_Synchronous->send('{"className":"J...', Array)
#5 /home/xxxxxx/public_html/om/application/models/File.php(209): Omeka_Job_Dispatcher_Default->send('Job_FileProcess...', Array)
#6 [internal function]: File->afterSave(Array)
#7 /home/xxxxxx/public_html/om/application/libraries/Omeka/Record/AbstractRecord.php(277): call_user_func(Array, Array)
#8 /home/xxxxxx/public_html/om/application/libraries/Omeka/Record/AbstractRecord.php(550): Omeka_Record_AbstractRecord->runCallbacks('afterSave', Array)
#9 /home/xxxxxx/public_html/om/application/models/Item.php(322): Omeka_Record_AbstractRecord->save()
#10 /home/xxxxxx/public_html/om/application/models/Item.php(235): Item->saveFiles()
#11 [internal function]: Item->afterSave(Array)
#12 /home/xxxxxx/public_html/om/application/libraries/Omeka/Record/AbstractRecord.php(277): call_user_func(Array, Array)
#13 /home/xxxxxx/public_html/om/application/libraries/Omeka/Record/AbstractRecord.php(550): Omeka_Record_AbstractRecord->runCallbacks('afterSave', Array)
#14 /home/xxxxxx/public_html/om/application/libraries/Omeka/Controller/AbstractActionController.php(144): Omeka_Record_AbstractRecord->save(false)
#15 /home/xxxxxx/public_html/om/application/controllers/ItemsController.php(149): Omeka_Controller_AbstractActionController->addAction()
#16 /home/xxxxxx/public_html/om/application/libraries/Zend/Controller/Action.php(516): ItemsController->addAction()
#17 /home/xxxxxx/public_html/om/application/libraries/Zend/Controller/Dispatcher/Standard.php(308): Zend_Controller_Action->dispatch('addAction')
#18 /home/xxxxxx/public_html/om/application/libraries/Zend/Controller/Front.php(954): Zend_Controller_Dispatcher_Standard->dispatch(Object(Zend_Controller_Request_Http), Object(Zend_Controller_Response_Http))
#19 /home/xxxxxx/public_html/om/application/libraries/Zend/Application/Bootstrap/Bootstrap.php(97): Zend_Controller_Front->dispatch()
#20 /home/xxxxxx/public_html/om/application/libraries/Zend/Application.php(366): Zend_Application_Bootstrap_Bootstrap->run()
#21 /home/xxxxxx/public_html/om/application/libraries/Omeka/Application.php(79): Zend_Application->run()
#22 /home/xxxxxx/public_html/om/admin/index.php(28): Omeka_Application->run()
#23 {main}