Stop Mass Signups? PHP Form Security Checks?

Hi,

I was wondering where anyone can advise me how I would go about stopping automated signups for in PHP. I have seen systems where the script generates an image and the user types in the code that can be seen in the image.

I have searched the 'net but cant seem to find anything...

How do I do this?

TIA
Paul
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pnh73Asked:
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scully00000Commented:
If you are running PHP on Linux:

1. Get Zlib from wherever you get your libraries from (e.g. www.redhat.com). Install it.

2. Get libpng and install it.

3. Get Freetype and install it.

4. Compile the GD library.

5. Recompile PHP with the following options:
--with-gd=/usr/local --with-png-dir=/usr/local --with-freetype-dir=/usr/local --with-zlib-dir=/usr/local (replace /usr/local with wherever you installed the libraries)

Check PHP works.

Add a function like this:
function randomimg($numstring)

{
$im = ImageCreate (300, 40);
$grey = ImageColorAllocate ($im, 230, 230, 230);
$black = ImageColorAllocate ($im, 0, 0, 0);

ImageTTFText ($im, 20, 0, 10, 25, $black, "arial.ttf", $numstring);

ImagePng ($im);
ImageDestroy ($im);
}

Generate a random number string by your choice of method and pass it to this function.

Cheers
pnh73Author Commented:
I need a way of doing that doesnt require a linux base or a recompile of PHP as I will probably be serving the site from shared hosting and maybe not even off Linux (much to my dislike, but its the choice of my client).
shmertCommented:
Do a google search for "CAPTCHA".  http://www.captcha.net/

Note to scully:  I think a good captcha system will distort the images some, so OCR (Optical Character Recognition) systems can't decipher the image.  One low-tech way to do it would be to create your own alphabet of scrambled images, and then assemble them using <img> tags.  Just don't name the images anything obvious like 's.gif' or something.

Then, display a string of these images which spell out a word, and have the user registering type in the text to authenticate that he is, in fact, human.

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pnh73Author Commented:
After a little bit more searching with the aid of the post from shmert i found the follwing which looks like it will work :D

http://www.planet-source-code.com/vb/scripts/ShowCode.asp?txtCodeId=739&lngWId=8

Thanks

Paul
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