do you get any error messages in the debug output (clear the cache before checking that to make sure that ez creates the pictures again)? Also go to the var/<site_access>storage/images folder and check there for a few pics whether the image variations are created there.
Alright! I have checked the debug messages a little bit closer than before. ;-)
And there are two warnings which explain, why conversions do not work!
Warning: eZImageManager::convert
The filter 'geometry/scaledownonly' is not supported by any of the image handlers, will ignore this filter
Warning: eZImageManager::convert
The filter 'geometry/scale' is not supported by any of the image handlers, will ignore this filter
I had a closer look on GD installation. And when running a test script following error message is appearing: Fatal error: Call to undefined function: imagecreate()
When I found the cause of this installation problem, I will post it as reference.