We use Sophos AV, too, and before sysprepping and pulling the image I uninstall Sophos AV, but just the program itself, not the Auto-Update application, which is separate.
After putting the image on another PC, Sophos AV is automatically installed via the Auto-Update, that was still on the image (including the update information, i.e. where to download it from). Has always worked for me this way.