Basically in the HelperPHP.php file in the WA_DigitalFilePro directory on your site, you will need to find the WA_DFP_ResizeImage function. In that function for the setting you have set up, you will have to modify the imagecopyresampled function calls so that the image isn't placed at the top left of the new image by calculating the correct location to put it instead. The third and fourth parameters to that function call are the x and y locations to place the image.