inconsistent and unpredictable 403 responses for image script

[sneakyimp]

I've got a page with an elaborate javascript in it (imageflow) that is meant to emulate the apple coverflow that you see on iPhones. It wasn't my idea to use it but I must fix it.

This elaborate javascript, in order to show reflections of an image, makes use of a PHP script that will take an image as input, invert it vertically and create a reflection image dynamically. The script is called reflect2.php.

The problem I'm having is that the reflect2.php script is unpredictably returning 403 (forbidden) or 404 (not found) errors sporadically. The behavior will vary for a given image so it's apparently got no relation to the image format. For example, I will load my page and I'll get some 403/404 for certain urls (which correspond to images in my page):

FIRST ATTEMPT - only one bad reflection image
http://mydomain.com/reflect2.php?img=product_images/ReynsRedemption_72SM.jpg&bgc=e3d8c7

The second time I load the same page, that previously broken image will be fine but this other one will be broken
SECOND ATTEMPT
http://mydomain.com/reflect2.php?img=product_images/Everlong_72SM.jpg&bgc=e3d8c7

The third time, all the prior images are fine and this image, which was fine before, is not 403:
THIRD ATTEMPT
http://mydomain.com/reflect2.php?img=product_images/TrustMeIfYouDare72LG.jpg&bgc=e3d8c7

I don't know why a given request to reflect2.php might result in a 403 reponse. As far as I can tell there is no code in the script that would result in such a header being sent for any reason whatsoever. I'm wondering if this might be a problem with Apache somehow. I'm on thin ice when it comes to Apache configuration values but perhaps there's a limit in the simultaneous connections permitted, the number of PHP threads available, or the keep-alive values or something?

Any thoughts about how to solve this would be much appreciated. Tomorrow is launch day 🙁

[bradgrafelman]

What do the lines from Apache's access/error logs look like?

[sneakyimp]

I can't find any:

grep -ir 'reflect2.php.* 403' /home/user4/access-logs/mydomain.com

This cmd returns nothing. There are a bunch of 404's in there though -- but that's what the script sends when it can't find the image it's supposed to process.

[sneakyimp]

Still having problems with this. This command returns 14,000:

 grep -i "reflect2.*200" store.mydomain.com | wc -l

this one returns 620:

grep -i "reflect2.* 404" store.mydomain.com | wc -l

this one returns zero:

grep -i "reflect2.* 403" store.mydomain.com | wc -l

I'm thinking that perhaps apache locates the reflect2.php script which starts running and then there's some kind of problem that occurs (permissions perhaps?) that ends up throwing a 403 error at some point.

Is there anywhere I could find such an error? in the PHP error log?

[sneakyimp]

Still wrestling with this (beastly) problem. There do appear to be errors associated with this breakdown:

[Sun Feb 13 18:21:53 2011] [error] [client 174.57.253.224] client denied by server configuration: /home/user/public_html/reflect2.php, referer: http://www.domain.com/index.php
[Sun Feb 13 18:21:53 2011] [error] [client 174.57.253.224] File does not exist: /home/user/public_html/403.shtml, referer: http://www.domain.com/index.php

I'm wondering if there might be an easy way to trap all errors no matter how small and write them to a log file.

[sneakyimp]

script tgz archive attached for reference.