Your Image Processor is totally a server issue.
As far as downloading 4.8d just sign in to the Photopost members area and download the latest one. There are upgrade instructions.
Basically you want to overwrite everything except the config-inc.php,header,htm,footer.htm and header-inc.php if your using it.
So unzip the file photopost48d.zip on your hard drive after downloading say to a directory gallery. Delete the following 4 files from the distroibution so you do not overwrite your good files on the server. FTP to your server and upload the new photopost files to the one on the server overwriting the files. Remember you have already deleted on your hard drive any files that would cause a problem so your good to go. Once finished you should be up to 4.8d
If your savvy enough with FTP to just read the changedfiles.txt in the documentation folder you can upload just the changed files