Validated XF Owner
No, the image names are stored in the database and if you blow away all images, the movies with current posters will not have a replacement poster suggested when you check for a new poster.You must validate your XenForo license to see quoted content
If you clear the database of all image names, you'll have to manually check EVERY thread for new posters. You're better off checking only those with a problem.
EDIT: I am seeing a lot of threads that are not movie threads with the movie thread information being displayed in the forum thread list, but nothing for the movie in the first post of the thread. I would be curious how that might be possible.