This will most likely involve building a custom PHP script to do this.
The first part of the script would do the audit to compile a list of all files currently in use in the various fields. You'd need to tell the script which columns hold the image data.
The second part of the script would run each file name against that list and delete the file from the filesystem if it's not present.
Once the script has run, you should purge your CE Image cache directory to remove all unused files. CE Image will regenerate newly re-sized files as needed.
Back up the database and all files before starting this process.
If you aren't able to write such a script yourself, there are many talented developers in the EE community who can. I have someone to suggest if needed.