This is not answering the exact question you posed, but as as far as I am concerned, your current attempt is the wrong approach to solve the problem of wrong image paths after moving anyway.
Rather than what you are attempting to do, either replace the image paths in the database, or redirect those.
While replacing/updating image paths can be done manually, there’s (a minimum of) two excellent plugins that will do the job. Take a look at either
- Velvet Blues Update URLs
- or @Bueltge’s Search and Replace
As for rewriting the paths, see the Redirection plugin. Also fairly simple to use.