Welcome, Marc.
The
Images by ID utility described
here is what you're looking for. You will need to assign ID's using the
Reindex movies tool. Hopefully, you've imported the poster location. If you haven't, you will need to do so. Then export ID and poster location to Excel, and use this to create a DOS batch file that will rename all your posters to ID (i.e.,
rename [full pathname of poster] [ID].jpg).
Before importing, make sure
Preferences - Miscellaneous - Save images in database is
not set. When using the utility, set the
Thumbnails folder to something different than the
Image folder (or the images will be overwritten by thumbnails). After successfully importing, I recommend then setting
Save images in database.
I tested this undocumented utility for the first time just now and found it a bit tricky, so please practise on a copy of your database until you're sure you've got it right. Good luck!