check if string is image

Question

There is an image in string format, outputting that string with some mime type headers would be enough to render it on a page, how to check if that string is an image?

By "string format" do you mean base64? If so you should look into magic number libraries. (The most common of these is simply called "magic.") — OmnipotentEntity
– OmnipotentEntity, Commented May 19, 2012 at 8:48

josmith · Accepted Answer · 2012-05-19 08:48:33Z

11

"An image resource will be returned on success. FALSE is returned if the image type is unsupported, the data is not in a recognised format, or the image is corrupt and cannot be loaded."

Example:

<?php
$data = 'iVBORw0KGgoAAAANSUhEUgAAABwAAAASCAMAAAB/2U7WAAAABl'
       . 'BMVEUAAAD///+l2Z/dAAAASUlEQVR4XqWQUQoAIAxC2/0vXZDr'
       . 'EX4IJTRkb7lobNUStXsB0jIXIAMSsQnWlsV+wULF4Avk9fLq2r'
       . '8a5HSE35Q3eO2XP1A1wQkZSgETvDtKdQAAAABJRU5ErkJggg==';
$data = base64_decode($data);

$im = imagecreatefromstring($data);
if ($im !== false) {
    header('Content-Type: image/png');
    imagepng($im);
    imagedestroy($im);
}
else {
    echo 'An error occurred.';
}
?>

http://php.net/manual/en/function.imagecreatefromstring.php

answered May 19, 2012 at 8:48

josmith

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3 Comments

NT_ Over a year ago

You need to suppress errors using '@' or else you are doomed for that imagecreatefromstring() .

Timo Huovinen Over a year ago

@ngen Any way to avoid getting doomed and at the same time avoid using @?

NT_ Over a year ago

@YuriKolovsky You can't . Since you are trying to load a string into a function which is expecting an image. It will fail 1) if the image data is corrupt . 2) if it's not an image.

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