'imagecreatefrompng' is outputting a crashed image - php

Question

I’m having problems with gd library in PHP when I try to do a imagecratefrompng. I’m running a script where the user input a text and it is added to a pre-created image. Problem is, when I output the image the image show as broken.
Can anyone help pointing if something is wrong with my script/image?
The image is a PNG, 600x956, 220kb file size.
GD Library is enabled. PNG, JPEG, GIF support are enabled.
Here is the code.
// Text inputed by user
$text = $_POST['text'];
// Postion of text inputed by the user
$text_x = 50;
$text_y = 817;
// Color of the text
$text_color = imagecolorallocate($img, 0, 0, 0);
// Name of the file (That is in the same directory of the PHP file)
$nomeDaImagem = "Example";
$img = imagecreatefrompng($nomeDaImagem);
//Text is retrieved by Post method
imagestring($img, 3, $text_x, $text_y, $text, $text_color);
header("Content-type: image/png");
imagepng($img);
imagedestroy($img);

Answer 1

There are a number of issues with your script:
You attempt to allocate the colour to the image, before you have actually created the image.
Your string to be written is in the variable $nome, but you are printing $text.
You don't check if $_POST['text'] exists, which may result in a Notice-level error.
You don't check if the file exists, which may result in a Warning-level error.
Here's an example of your code, fixed:
// Text inputed by user
$nome = isset($_POST['text']) ? $_POST['text'] : "<Nothing to write>";
// Postion of text inputed by the user
$text_x = 50;
$text_y = 817;
// Name of the file (That is in the same directory of the PHP file)
$nomeDaImagem = "Example";
$img = file_exists($nomeDaImagem)
? imagecreatefrompng($nomeDaImagem)
: imagecreate(imagefontwidth(3)*strlen($nome)+$text_x,imagefontheight(3)+$text_y);
// Color of the text
$text_color = imagecolorallocate($img, 0, 0, 0);
//Text is retrieved by Post method
imagestring($img, 3, $text_x, $text_y, $nome, $text_color);
header("Content-type: image/png");
imagepng($img);
imagedestroy($img);

Answer 2

Read more:--
http://php.net/manual/en/function.imagecreatefrompng.php
http://www.php.net/manual/en/function.imagecreatefromstring.php
or try this
<?php
function LoadPNG($imgname)
{
/* Attempt to open */
$im = #imagecreatefrompng($imgname);
/* See if it failed */
if(!$im)
{
/* Create a blank image */
$im = imagecreatetruecolor(150, 30);
$bgc = imagecolorallocate($im, 255, 255, 255);
$tc = imagecolorallocate($im, 0, 0, 0);
imagefilledrectangle($im, 0, 0, 150, 30, $bgc);
/* Output an error message */
imagestring($im, 1, 5, 5, 'Error loading ' . $imgname, $tc);
}
return $im;
}
header('Content-Type: image/png');
$img = LoadPNG('bogus.image');
imagepng($img);
imagedestroy($img);
?>