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PHP Form image verification PDF  
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PHP Form image verification
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The code explained:

Create a php file random_image_sample.php. This file will generate the an image with a random 5 letters text.

//random_image_sample.php contents 

//start a session
//this function is called recursivelly
function random_string($len=5, $str='')
for($i=1; $i<=$len; $i++)
    //generates a random number that will be the ASCII code of the character.
//We only want numbers (ascii code from 48 to 57) and caps letters.

$ord=rand(48, 90);
if((($ord >= 48) && ($ord <= 57)) || (($ord >= 65) && ($ord<= 90)))
//If the number is not good we generate another one
return $str;

//create the random string using the upper function
//(if you want more than 5 characters just modify the parameter)


//We memorize the md5 sum of the string into a session variable
$_SESSION['image_value'] = md5($rand_str);

//Get each letter in one valiable, we will format all letters different

//Creates an image from a png file. If you want to use gif or jpg images,
//just use the coresponding functions: imagecreatefromjpeg and imagecreatefromgif.


//Get a random angle for each letter to be rotated with.
$angle1 = rand(-20, 20);
$angle2 = rand(-20, 20);
$angle3 = rand(-20, 20);
$angle4 = rand(-20, 20);
$angle5 = rand(-20, 20);

//Get a random font. (In this examples, the fonts are located in "fonts" directory and named from 1.ttf to 10.ttf)
$font1 = "fonts/".rand(1, 10).".ttf";
$font2 = "fonts/".rand(1, 10).".ttf";
$font3 = "fonts/".rand(1, 10).".ttf";
$font4 = "fonts/".rand(1, 10).".ttf";
$font5 = "fonts/".rand(1, 10).".ttf";

//Define a table with colors (the values are the RGB components for each color).

//Get a random color for each letter.
$color1=rand(0, 5);
$color2=rand(0, 5);
$color3=rand(0, 5);
$color4=rand(0, 5);
$color5=rand(0, 5);

//Allocate colors for letters.
$textColor1 = imagecolorallocate ($image, $colors[$color1][0],$colors[$color1][1], $colors[$color1][2]);
$textColor2 = imagecolorallocate ($image, $colors[$color2][0],$colors[$color2][1], $colors[$color2][2]);
$textColor3 = imagecolorallocate ($image, $colors[$color3][0],$colors[$color3][1], $colors[$color3][2]);
$textColor4 = imagecolorallocate ($image, $colors[$color4][0],$colors[$color4][1], $colors[$color4][2]);
$textColor4 = imagecolorallocate ($image, $colors[$color5][0],$colors[$color5][1], $colors[$color5][2]);

Write text to the image using TrueType fonts.
$size = 20;
imagettftext($image, $size, $angle1, 10, $size+15, $textColor1, $font1, $letter1);
imagettftext($image, $size, $angle2, 35, $size+15, $textColor2, $font2, $letter2);
imagettftext($image, $size, $angle3, 60, $size+15, $textColor3, $font3, $letter3);
imagettftext($image, $size, $angle4, 85, $size+15, $textColor4, $font4, $letter4);
imagettftext($image, $size, $angle5, 110, $size+15, $textColor5, $font5, $letter5);

header('Content-type: image/jpeg');
Output image to browser
Destroys the image