lucy24 - 9:07 am on Nov 9, 2012 (gmt 0)
You could replace the [F] with a rewrite to your image of choice. You would have to allow them to get the page itself, and only apply the rewrite to requests for images.
This only works if the human pinner has the (real) image in their cache, so they don't realize the wrong thing is getting pinned when they look at the preview page. Otherwise they would just cancel the whole process.
Option 4. (from my own htaccess) is
RewriteRule \.(jpe?g|gif|png)$ /pictures/smallgifs/onedot.gif [L]
where onedot.gif is a 1x1 transparent gif that's used for a variety of purposes. People can pin to their heart's content, but it won't do them any good because nobody will see anything.