creating images with text in

paulg

Hi guys,

I've seen on some sites, an image with some random text or number in it, where the user is asked to input the text or number they can see in the image. This is a security feature to stop automatic/robot form entry. You've probably seen this in loads of places.

WELL, I want to do something along the same lines, so can someone please point me in the right direction? :p

I tried searching the PHP resource sites, but I'm not sure what to call it.

austinderrick2

Try using the random function and make several images to start with...

<?php
$random_image_name = rand(0,1000);
echo "<img src=\"$random_image_name.gif\">";
?>

dta

using rand 0-1k is the same point, but making 1000 images is a waste.. just make images 0-9, or a-z

then do the same method of puting them together but by pieces like

<img src=a><img src=0><img src=b> so the key is a0b then check for that

hope that helps

Moonglobe

the really advanced ones use image crate functions (like the GD library for PHP) and pass around a key in a hidden field. i read how to do it once..... its ver complex, and involves a DB.

examancer

its not too hard really. the info on how to create an image with text in it is easily accessible. beyond that, the only problem you would run into is making the text random, and then when they type it in, being able to verify that its right.

You could do this using sessions or cookies.... take the unique identifier of the user (the session or cookie value) and store it in a database along with some random text.

Then, on the form, call a PHP file in the image tag, and have that image script pull the text back out of the database and put it in the image.

When the user submits the form, pull the text from the database (again using the cookie or session value) and make sure the values match. There ya go... secure registration script that can only be filled out by a human, or at least makes the idea of a computer filling it out many times more complex.

dta

you could always store the md5() value somewhere so even if "it" reads the source it will not know the value (they are there to protect from those bots right? and im sure bots won't waste their time trying to brute force md5)

thats just an alternative from cookies/sessions/etc..

paulg

Thanks guys.

I want to do the whole GD thing. I wrote some code and it works okay.

But, I remember reading an article somewhere about it where the programmers overlaid the image with a 'scratch' line effect to stop any program capable of 'reading' the image. I tried a 1px line across the image but sometimes it makes the whole thing difficult to read.

How do I do this with user defined fonts and sizes instead of the built-in text sizes?

OR BETTER STILL - does anyone know where that article was published? It was on the 'net somewhere.

Cheers all.