I confess, I picked up the pack() code from a Perl font making script somewhere. Looking at your code, I was guessing that’s how numbers bigger than 255 would be handled, so I went looking for confirmation and found that.

Thanks for writing the original code.

Antone

Thanks for the kind words about my script. T’was written a long time ago, and I’m glad you found a use for it.

I like your use of pack() for the header.

I noticed you changed the inner loop from using $c to calling chr(). In this kind of application the difference is absolutely trivial, and it’s probably worth doing it your way for clarity of code, but I ran some benchmarks looping 100000 times, first running $d .= chr(255); and in the second loop running $d .= $c; where $c=chr(255); Results below:

chr() in loop: 0.173…
$c in loop: 0.031…

Now, like I said it’s a totally trivial difference and not really worth thinking about, although it will loop 23400 times assuming 26 characters @ 30×30, so there might be a marginally noticeable difference (benchmarks for 23400: 0.045… vs 0.007…)

But I thought I’d just explain why I did it that way :0)

I also wrote a captcha script you might like to take a look over: http://www.puremango.co.uk/2005/04/php_captcha_script_113/

Have fun!