In C# I am able to use Microsoft.Office.Interop.Powerpoint to export .ppt slides as images but it MS Office should installed on the computer.
It appears that there is an automation API for OpenOffice, forums but I didn’t find any script on PowerPoint to images using VB Script?
with OpenOffice, the best way to automate the export I found some time ago, was to automate the "save as HTML" and use the images from this export.