It would make just as much sense to load a whole collection, filter for the files to treat and then use MP3tag's functions to do that. And as this could include many more steps than just the call of a single function, I would see that as superior approach. It would be interesting to see how you found out the size of an embedded picture in an audio track just by looking at it with the Windows Explorer...
MP3tag has no command line parameters to call actions. The idea BTW has been discussed since 2005: