Is there a method (other than trial and error) I can use to find unused image files? How about CSS declarations for ID's and Classes that don't even exist in the site?
It seems like there might be a way to write a script that scans the site, profile it, and see which images and styles are never loaded.
You don't have to pay any web service or search for an addon, you already have this in Google Chrome under F12 (Inspector)->Audits->Remove unused CSS rules
Screenshot:
Update: 30 Jun, 2017
Now Chrome 59 provides CSS and JS code coverage. See https://developers.google.com/web/updates/2017/04/devtools-release-notes#coverage
At a file level:
use wget to aggressively spider the site and then process the http server logs to get the list of files accessed, diff this with the files in the site
diff \
<(sed some_rules httpd_log | sort -u) \
<(ls /var/www/whatever | sort -u) \
| grep something
I seem to recall either Adobe Dreamweaver or Adobe Golive having a feature to find both orphaned styles and images; can't remember which now. Possibly both, but the features were well-hidden.