How to get a 404 logged with try_files?

[monster]

Hi! Just started with Nginx after reading it reached 1.0.
Congratulation!

I'm trying to get my test site to return a "missing image" icon when an
image is missing, but have a 404 logged so I know I messed up something.
I want to specify the images name without file extensions, in case I
move some from PNG to JPG, or the other way around. My problem is that
try_files doc says last path MUST exist. I would like last path to be
$uri and cause a 404, not a 500. Tried using error_page to convert 500
to 404, but did not have any effect. Thanks for any advice!

location ~ ^/img/[^\.]*$ {
    try_files $uri.png $uri.jpg $uri.gif $uri;
    error_page  500 =404	/img/missing;
}

location /img/ {
    error_page  404		/img/missing;
}

location = /img/missing {
    rewrite .* /img/icon/missing.png;
}

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,194965,194965#msg-194965