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    <p>The first thing you should do is determine whether mod_rewrite is in fact part of the problem by accessing one of the failing URLs directly via its rewritten form and verifying that you get the expected result.</p> <p>Indeed, the problem might simply be that the PHP script for the smaller resolutions "doesn't work" while it does for the original size ones. The first of the following URLs nicely served me an image; the second one is supposed to give me a smaller version of the same image, but served me an HTTP 500: </p> <pre><code>http://106.186.21.176/images/controller/Resizer.php?m=original&amp;a=q&amp;e=png http://106.186.21.176/images/controller/Resizer.php?m=small&amp;a=q&amp;e=png </code></pre> <p>I got the same result (HTTP 500) for any of the smaller-size format names mentioned in your post, which matches your problem description.</p> <p>Once you've verified that the script works as expected, it's likely that the problem is with mod_rewrite. If so, enable rewrite logging: use the <a href="http://httpd.apache.org/docs/2.2/mod/mod_rewrite.html#rewritelog" rel="nofollow">RewriteLog</a> directive to activate it, and <a href="http://httpd.apache.org/docs/2.2/mod/mod_rewrite.html#rewriteloglevel" rel="nofollow">RewriteLogLevel</a> to control its verbosity. Especially at the higher log levels, it can give you very detailed information about exactly what it's doing. This should make the problem readily apparent from the logs.</p> <p>Also, if possible, try to avoid configuring mod_rewrite rules in .htaccess files -- move them into your main server config file instead. The reason is explained on <a href="http://httpd.apache.org/docs/2.0/rewrite/rewrite_tech.html" rel="nofollow">Apache mod_rewrite Technical Details</a>, section "API phases":</p> <blockquote> <p>Unbelievably mod_rewrite provides URL manipulations in per-directory context, i.e., within .htaccess files, although these are reached a very long time after the URLs have been translated to filenames. It has to be this way because .htaccess files live in the filesystem, so processing has already reached this stage. In other words: According to the API phases at this time it is too late for any URL manipulations. To overcome this chicken and egg problem mod_rewrite uses a trick: When you manipulate a URL/filename in per-directory context mod_rewrite first rewrites the filename back to its corresponding URL (which is usually impossible, but see the RewriteBase directive below for the trick to achieve this) and then initiates a new internal sub-request with the new URL. This restarts processing of the API phases.</p> <p>Again mod_rewrite tries hard to make this complicated step totally transparent to the user, but you should remember here: While URL manipulations in per-server context are really fast and efficient, per-directory rewrites are slow and inefficient due to this chicken and egg problem. But on the other hand this is the only way mod_rewrite can provide (locally restricted) URL manipulations to the average user.</p> </blockquote> <p>In general, not using .htaccess at all has the added advantage that you can tell Apache to not even bother and disable the functionality all together, which save Apache from having to scan each directory level it serves from for the .htaccess files.</p>
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    1. COThanks you for the answer. I was a bit confused by the script and its way of generating links (I am not the author), so it didn't come to my mind to check out those exact links without rewriting. So, upon that realization that something might be wrong with the script itself, I checked some logs too, and found something I missed before, PHP errors. There we calls to functions that didn't exist, and I found the cause to be the missing GD library. Again, the authors of the script haven't stated that is being used, so when I installed it everything worked as expected.
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