Based on the error message you are getting, it appears that Alfresco is unable to find the ocr.exe application when it tries to call it to perform the transformation. I would suggest adding the location where you have the ocr.exe application to the system path (be sure to restart Alfresco using a new command window that has the new path), and see if that helps. If you are still having trouble, please provide your Alfresco version in a future post, since some of the Spring configuration files may need to be modified depending on your version.
Kevin Dorr
Alfresco