Deleted photos continue appearing in screensaver
I can't reproduce your problem in Mavericks or Mountain Lion; if I add an image to the watched directory and start the screensaver, the new image appears; if I delete the image and restart the screensaver it disappears. So a logout/login cycle and/or restarting the Mac seems called for.

But if those fail, I saw a similar issue some years ago that resulted from a corrupted screensaver preferences file, and you could try solving it the same way: Try flushing the screensaver preferences by deleting the plist file.

To do that, in the Terminal, run the following (quit System Preferences first):

rm -i "$(ls -t ~/Library/Preferences/ByHost/com.apple.screensaver.[0-9A-F]*.plist | head -1)"


The -i is for safety; it should ask if you want to remove a single file, like this:

remove /Users/trey/Library/Preferences/ByHost/com.apple.screensaver.65BC01F5-7A67-5B3E-9193-9464C78533AD.plist?

Confirm by pressing y and return. If it asks to remove a file that doesn't look like that, or tries to remove more than one file, press Control-C to abort.

Now re-open System Preferences, select the screensaver again and point it at the Dropbox directory again. The screensaver should now update normally.