Am Thu, 14 Jun 2007 15:51:10 -0400
schrieb Forest Bond <[EMAIL PROTECTED]>:
> You can do it without external persistence (sessions and/or database
> table) by encrypting the correct response in the image filename.
So when the request to get the image is sent to django, we have to
decrypt the solution according to the image's URL. In my
opinion that raises some problems, because it could be decrypted by
someone else too, unless you use a private/public key encryption,
which means more work on the django server than using just hashed
filenames like my approach does.
Furthermore I don't see a real reason to generate images on the
fly instead of storing them directly. My approach is quite speedy even
with auto_cleanup, when there are many captcha images sitting in the
filesystem all the time. I ran an apache benchmark test on my
development machine (not the fastest hardware) multiple times where
each of them creating 1000 captchas:
With auto_cleanup:
captchas on disk at start Requests per second
first run 0 22.82
second run 1000 13.06
third run 2000 9.16
fourth run 3000 7.02
Without auto_cleanup:
captchas on disk at start Requests per second
first run 0 39.05
second run 1000 39.45
third run 2000 37.27
fourth run 3000 38.46
disk space used for 4000 captchas: 48MB
And these are really extreme cases, since they imply that no one of the
1000 visitors in each run ever submits a form back, so its captcha image
would be deleted automatically.
If you really have concerns regarding speed, you might use a cronjob
that deletes the old captchas in the background, so the whole system
stays very responsive.
If you have a compelling reason why this solution is bad, I'll be happy
to know. Otherwise I think, I'll stick with images in the filesystem.
In my opinion it's fast for most sites even with auto_cleanup, and for
really high volume sites just disable auto_cleanup, use your own
cronjob, and everything should be ok. Right now, I just can't see a
benefit in using images created on the fly.
Martin
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